Hunters are a hard class to really describe due to one key factor, there are many good Hunters and for every one of them there are 5 bad Hunters. Its amazing the number of Hunters that reach level 70 not realising the benefits, flaws, and potential of their pets and traps, unfortunately when Pugging you are likely to encounter many of these and are likely to come off with a bad experience from the class. Its not true though, Hunters can do some really amazing things and can really make or break a party as they should be counted on to do a lot of things. Breaking down Hunters is relatively simple, their Pet is a good dps, can be used for misdirections to pull mobs away from the Tank to tank / CC the mob or can be used straight up as an off-Tank, in the latter role a Beast Mastery Hunter is much better equipped for this than the other forms of Hunter, you can effectively use a Hunter in any role, DPS, Tank, CC (or the infamous Resto-spec Hunters) and they will perform well.
Hunters tend to complain about not getting buffs, about not getting an ideal group setup, about basically anything they can, its a bit of a game really as people tend to assign buffs and groups wrongly to hunters. Hunters don't really offer any buffs to the party directly, its passive abilities and in-combat marks that allow them to really shine.
Hunters are very self-synergistic, depending on spec they can boost the dps of their party by 3% (stacking!), offer improved marks, etc. Typically place hunters to fill slots where needed, a caster group won't really benefit a hunter (barring the shadow priest), but if he has the dps buff he does benefit the caster group. Aiming for a Shaman with an agility totem will also help Hunters a lot, and some kind of mana source if possible (never above casters) will allow them to maximise their dps. They don't really fit into a melee group due to wanting different totems (and the melee group typically being quite full), so in preference they go into:
Crit Bear Groups
Stacked Hunter Groups
Caster Group with Mana Regen
Basically give the Hunters as much benefit as you can, and assign their buffs to help others, but place other more beneficial classes first, don't drop a Retribution Paladin from a melee group for a Hunter who will benefit less. This is a kindof misunderstood aspect, since Hunters are very capable DPS, however as both Warlocks and Rogues are likely to be higher DPS overall you must consider this, and stack groups preferentially for those classes first, meaning that Hunters will tend to be used as a filler class (which is ok, as they are self-synergistic and benefit beautifully from being in a group with a Druid tank).
There is an issue of contention about Hunters, the correct order for Blessings is:
Blessing of Might
Blessing of Kings
Blessing of Wisdom
Blessing of Salvation
Blessing of Light (if multiple Paladins present)
Blessing of Sanctuary
The first two are typically interchangeable and depends on your Hunter's preference, I won't discuss why since I don't really know or for that matter care since they both increase DPS. The ordering of Salvation though is under debate, and frankly shouldn't be, it can be applied for the first 30s or so of a fight then swapped out if needed, however the use of Feign Death allows Hunters a full aggro-wipe every 30s (if not resisted) meaning its a bad tank that can't keep ahead of a good Hunter, or rather a good Hunter can easily stay below a bad tank. If you have a Hunter demanding Salvation ahead of DPS increasing buffs (and yes Wisdom does increase DPS as it reduces the need for mana stings, pots etc), you need to look at the Hunter carefully, a good Hunter doesn't want it in preference, and a bad Hunter will over-aggro anyway (even if it means breaking cc to do so :P).
There are situations where Salvtion is more important, the first 30s or so of a fight where the tank is building up a threat lead, fights like Void Reaver with aggro-dumps and tight limits, however these are not your regular situation, as a rule of thumb Salvation is the 3rd dump Blessing for Hunters, use common sense and get good Hunters (and yes I met some that didn't use Feign Death because it dropped their DPS... apparently more so than being threat capped and not doing anything anyway). Salvation is a tool, never see it as something Hunters shouldn't get, but consider first Feign Death and the tank's TPS curve, if thats ok then Salvation drops a lot down the list.
Hunters are a crowd control class, they have multiple forms of crowd control, Traps (slow or freeze), kiting (slow + aggro the mob in a big loop), and Pet Tanking, all 3 are very useful and should not be underestimated. Firstly traps, typically these can be used in two ways, firstly pulling a specific mob to the side of the pull line (or running up to a caster and dropping it under them) and trapping there, or placing the trap in the pull line, and letting Lady Luck decide what gets trapped. Both are valid methods of trapping, and the key here is to make sure the tank can see the trap, and can act on it if the trapped target breaks early or avoids the trap (on a non-specced Hunter the trap cooldown and duration are similar making chain trapping slightly riskier without acquiring aggro on the target, eg: the side pull). This form of crowd control is very reliable and should be assumed to function a lot like a sheep, a good Hunter can maintain their trap and not lose much personal DPS (if your Hunter runs out of melee, traps, then runs back in to hit things with his swords, he is losing a lot of DPS, but at that point his DPS probably isn't high anyway). Traps are very versatile, however only a single trap can be used at a time, so you must determine if its more important to freeze an enemy in place, or to slow a group of them and have the Hunter kite the target until his trap is up again. Traps are broken by AoE damage, meaning trapping within the tanking area will cause it to be broken.
Kiting is used on targets that cannot be controlled, instead the Hunter builds sufficient aggro on the target to make sure if follows them, then applies slowing shots and disorientates to make sure the target follows the Hunter but does not damage them. This technique will typically take the Hunter out of the fight from a DPS perspective, however will relieve a lot of pressure on the tank and healer as one more target is fully removed from combat. Using this technique should be easy for most good Hunters, its something they can easily practice as with chain trapping and it is a powerful solo ability as well. Unfortunately this requires a reasonably large space to be performed (the mob must remain beyond its hit range at all times and the Hunter capable of damaging it to maintain aggro), meaning that small cramped instances such as Shattered Halls can make this ability less useful (though you can use the length of the instance there instead if required).
Pet tanking is a highly subjective role, it can be useful as a backup to the actual tank in a 5-man instance, or in the case of tank death it can buy long enough to finish the fight. Typically however most Hunter pets are DPS based, and do not have the health and armour to survive long (its like using a Restoration Druid to go Bear form, it works, but isn't advisable in the long run). Many pets have an ability known as growl, which functions a lot like a taunt / aggro generation mechanic, while soloing this allows Hunter Pets to hold the target at a distance allowing it to be shot, in a tanking situation this allows the Hunter Pet to die horribly very quickly, slow the actual tank's threat generation and generally upset the group. Pet tanking should not replace the tank, but rather work in concert to provide DPS or the seconds needed to recover from a bad situation. One good aspect of this is that a Hunter can leave their pet far behind the group and misdirect to it, leaving one target running far from the group and while the pet is likely to die, the target is "controlled" for a reasonable length of time.
Combat and Utility:
The bread and butter of your Hunter, and here the spec of the Hunter makes the largest difference, typically Hunters stand at range ( > 5 yards) and maintain constant bow / gunfire at the target, more than any other class Hunters are defined by their weapon. Typically a pet will also be employed as a melee combatant and should be watched by the melee healers if possible as it will contribute 10-30% of the Hunter's overall damage (especially if Beast Mastery).
The typical raiding spec is Beast Mastery as it suffers from threat problems less due to splitting the damage more evenly between Hunter and Pet, and gives every party member a 3% damage bonus while the pet is active, Marksman gives a 125attack power buff to the party on a critical hit, and Survival a 25% of their Agility to attack power for the whole raid on a crit. This means that typically it is best to stack Beast Mastery Hunters with a single > 500 Agi Survival Hunter in the group (at lower than this the Marksman ability gives more AP to the group), again the benefits of a stacked Hunter group become apparent, 5 BM Hunters give their party +15% damage, a bonus rivalling that of Improved Shadow Bolt, except with guaranteed uptime.
In most raid situations Hunters will not perform their crowd control role, and will instead be simply a DPS class, they have a very weak AoE ability or two, however can hit multiple targets at once using multi-shot (3 targets). A good Hunter should however be on the ball and prepared to utilise their control abilties and pets to maximise the survival chance of the raid when something goes wrong.
Feign Death will allow Hunters to survive a wipe, though being to pre-emptive on this can turn a very narrow victory into defeat, Hunters must be careful to use this survival technique only when needed rather than trying to ensure their repair bill is lower than it would otherwise be.
Misdirection and Feign Death:
Good Hunters can be identified readily by their use of these abilities, Misdirection adds the Hunter's threat to the targets for a short period, and Feign Death, if not resisted, results in a complete Threat reduction on the Hunter, and can be used to save them from a wipe. Misdirection allows a Hunter to open a pull at its full potential as the threat is initially applied to to the Tank (or an unsuspecting DPS / Healer if they are cruel), or can be used mid-fight (on a 2 minute cooldown) to give a slight TPS boost to the Tank. Using Misdirection as a Threat boost works very well in Off-Tank situations where the Tank may be Rage / Mana starved, or have suffered a knock-back in threat, this means it is not directly a threat booster but a threat leveller, which is the intention of fights like Void Reaver, Gurtogg Bloodboil etc. In a single Tank situation it is typically applied as a direct Threat boost.
Misdirection pulls are used within Tier 5 and Tier 6 instances to allow for better positioning of bosses (who may otherwise force the tank to move, potentially opening up their back if the AI interprets a move as too long resulting in high damage / crushing blows), or for ranged pulls. An example of a ranged pull can be found in the initial parts of Tempest Keep where Falcons and Falconers wander in Al'ar's room, Misdirecting to a Tank gives initial aggro (and pulls them down the corridor) while a Feign Death immediately afterwards moves the Falcons aggro onto the Tank as well, pulling the group with no deaths and no risk of a bad knockback.
In boss fights with Adds it is also beneficial often to save the Misdirect as an additional pulling tool to move targets from Healers / DPS onto a positioned Tank (again the Al'ar fight is a good example). This ability allows a Hunter to save an overaggroing healer by moving their attackers, or indeed simply boosting the threat of the Add tank in a multi-target way. As with many abilities the potential of this skill is in the hands of the Hunter, and it can save many wipes and heart attacks as things go wrong due to its long ranged nature, and reasonable cooldown.
Tier 4 Level:
At this level Hunters are a great spot in any group or raid, they provide solid damage and their CC abilities and pet make them very valuable. Typically their damage will be reasonable at this level, however due to the early availability of crafted epics for Tailors, the cloth damage classes are likely to be higher. Encounters such as Magister's Terrace are very well suited to having Hunters in the group as they provide a backup crowd control source (or a primary one), yet retain enough armour and avoidance to survive should targets get loose.
Tier 5 Level:
Hunters typically at this level start to become one of the Higher DPS classes, having gained a good amount of gear and a much better weapon they can maintain it for an almost infinite period of time due to low relience on external sources of mana and consumables. Muiltiple fights at this level are not Pet friendly however and can result in a DPS drop from the Hunters, typically a good healer will manage to maintain their pets sufficiently to keep up damage.
Tier 6 Level:
Hunters drop down the damage tables here as Warlocks, Mages and Rogues really come into their own again. Hunters are still a very good class to bring along, and not much can really be added to the list. Essentially, if in doubt, a Hunter isn't a bad choice for any tier or instance, their health and armour make them survivable in fights like Naj'entus and their ranged DPS capability makes them good soakers for Bloodboils.
Tier 6 fights begin to become very aggro and threat dependent, meaning efficient use of Misdirection to the Tank or Off-Tanks becomes a very beneficial raid-wide utility (thought they should have used it in prior tiers, at this stage it becomes very valuable), and Feign Death becomes virtually required on many fights such as BloodBoil where it allows Hunters to keep up a near full threat rotation even through knockbacks and requiring multiple tanks to stay above the DPS with little incoming damage (Warlocks for example are much more threat limited here).
As with previous Tiers there is no reason a Hunter is a bad choice at this level, they have high DPS potential and good backup abilities in their crowd control and synergistic buffs. Stacking Hunters within a Tank group can become beneficial to the Tank due to these buffs giving an additional threat boost (and finding a very beneficial group for them). Typically at this stage a Warrior maintaining sunder or a Rogue using Improved Expose Armour is very beneficial to their DPS, with a single Hunter being nearly capable of offsetting the Rogue DPS loss to apply the IEA debuff.
Trapping is an art form, in general there are keys to it:
Trap in front / to the side of the Tank
Pull Early, pull efficiently
Learn to kite the mobs
Be prepared to sacrifice a trapped mob to save a healer
Trapping is one of the most "independent" actions in a party, typically the Tank begins the pull and the Hunter pulls from the tank towards a trap, this should be maintained in front of or to the side of the tank to allow them to keep an eye on it in case it breaks. Traps are very reliable, they can be replaced, repositioned and the Hunter can kite the mob if it cannot be re-established in time. Care should be taken to kite around and back to a good position if the target is breaking. Let the tank know whats happening, if you save the Healer and your other trap gets free we will be upset (and happy) because we can't see everything, a quick heads up lets us acquire the trapped mob for at least the duration of saving the healer. Take the initiative here, if its marked do whatever is needed to keep it for the duration and be careful to make sure that its not in range of AoE attacks.
A typical pull can be described in terms of a) Pull Corridor, b) Minimum Control Zone, c) Tanking Area, d) Kite Path. The pull corridor is the distance in a straight line between the target and the tank, this is the path that targets will take towards the puller and as such is safe for trapping in to guarantee one mob trapped, typically if a target is to be trapped it is best to do it to the side of the pull corridor initially to make sure that a failed trap can be pulled into the Kite Path rather than into the Tanking Area. The remaining zones can effectively be described as concentric circles, the Kite Path, then the Minimum Control Zone (where AoE tanking won't hit controlled targets) and the Tanking Area itself, typically the Healers are positioned in the rear 120 degrees of the pull directly away from the pull corridor, and the Minimum Control Zone. As the most mobile of control classes Hunters should pay attention to this idea and follow it, a target a Tank cannot see is one the Tank will likely try to find and engage, effectively stealing the controlled mob, keep targets that aren't being kited in the line of sight of the Tank and keep talking, let people know where you are, and what state the enemy is in.
As a reasonable explanation of the pull itself I present my own home made graphic, hopefully this gives some better idea of what I actually mean by the pull corridor and where it is safe to CC and stand.
While this diagram is crude and not to scale it shows the general idea behind the theory, the Tank is in control of their AoE area, and to reach a Healer or ranged DPS class not involved in kiting a target must go through this area, becoming vulnerable to melee range abilities and taunts. Sheep and other ranged Crowd Controls can be reapplied by stepping into the Tank AoE area, reapplying, then stepping back, or if in the minimum range area by simply reapplying it.
Hunters can easily trade blows with ranged classes using this technique by standing in the Ranged / Healer area, however may find it beneficial to be inside the control zone, or the kite zone to allow reapplication of traps and suchlike to require less movement. Again the reasonable armour and kiting capability of the Hunter class means that they are typically not watched as closely by the Tank as they should survive / Feign Death / Trap / Growl their way out of a threatening situation at least for a short time, meaning a Tank can focus on them only if needed rather than having to be as proactive as on cloth based DPS classes.