In group play each class has its own role, something special they bring into the group. In fellowships and small fellowships, the roles are somewhat flexible and you see many different group combos. However, in raids classes usually act according to their main role. This is a direct result of raids being the hardest group content in game - each class performs its main role best, which of course means higher changes of success. For example, it is rare to see dps guardians in raids. That is simply because a) some other class like hunter or champion makes a better dpser b) guardian makes a better tank than some other class that could also tank like captain. When everyone does what they can do best, the group is at its strongest.
Make sure you know which role you’re filling in the raid, trait and gear according to it and keep it as your primary interest. With primary interest I mean that your role is what you should focus most on while in the raid. For example if you’re a healer, healing is what you do. You might still be able to deal some damage etc in healing build, but don’t do so to the detriment of healing. If it’s a more quiet phase in the fight and everything is going smooth, feel to throw in some damage, but be prepared to switch back to healing the second it’s needed again. Same is true for every other role of course. Don’t let your primary role suffer because you’re doing something else instead - there are other people in the raid to take care of that something else.
Now let’s take a look at different class roles:
Dps (aka nuker, damage dealer) - Dpser’s job is to kill the enemies as fast as possible.
They can be split into melee dps (fights in close combat), ranged dps (attacks from range with a bow etc) and tactical dps (attack from range using magical attacks).
Damage can be either aoe or single target. Some instances have mechanics that make it unwise to use any aoe damage, so make sure which of your skills are aoe and which single target. It is also beneficial to be aware of the radius of your aoe attacks so you don’t accidentally hit crowd controlled mobs and wake them up.
For single target damage target nukers should always follow the rat (raid assist) target unless told otherwise.
Damage dealers’ secondary focus should be on threat (aka aggro or hate). Every damaging skill you use increases enemy’s threat towards you. The monster will attack whoever he hates the most (i.e. who has the highest threat). This should usually be a tank. Dpsers need to adjust their damage to the skills of the tank. Otherwise they are likely to end up dead for angry monsters beating on them. Many dps classes also have some skills that lower threat. However, if you get a mob hitting on you and can’t use any anti-threat skill to get rid of it, move closer to the tank, so he can more easily take care of it. Running away is usually a bad idea as it makes it hard for a tank to deal with the mob on loose.
Dpsers should usually position themselves behind a mob they are attacking. This protects them from enemies frontal aoe attacks and makes it impossible for enemies to parry or block their attacks.
Tank - Tank’s job is to make sure the enemies are hitting him and not his fellows and mitigate as much of incoming damage as possible.
Tanks use their high threat generating skills to keep enemies attention on them and thus protect other (more lightly armored) fellows from taking damage. Tank’s top priority should be to make sure the healer is safe - he can’t heal if he has mobs beating on him. Secondly a tank should keep mobs off dps classes. This, however, requires a bit of co-operation from the dpsers themselves, who should make sure they aren’t generating any more aggro the tank can manage to exceed. If a single mob with only a little morale runs off to hit a hunter for example, it’s probably best to ignore it and focus on other enemies - the mob will be dead in a moment anyways.
In addition to keeping mobs on him the tank should also try to minimize the incoming damage to make the healer’s job easier. This is done by making sure he has sufficient avoidances and mitigations and using his special skills like bubbles or avoidance boosts to reduce damage.
Healer - Healer’s job is to keep everyone else alive.
As with damage, heals can also be aoe. The difference here is that aoe heals don’t have max targets, but they only affect the fellowship of the healer (not the entire raid). Aoe heals tend to cost lots of power and have longer cooldowns than single target heals. Thus single target healing is usually the preferred way and aoe heals should only be used if several members actually need heals (as in case of heavy aoe damage by the mobs).
Power is often an issue for healers and learning to be power efficient is one of the characteristics of a good healer. Key is to avoid unnecessary over healing, healing people only when they’re actually loosing morale and using your smaller heals if someone just needs a little more morale
A healer should put the highest priority on healing himself and the tank. If either of them dies, it can easily result in a failure. In raids there are several healers and so healer’s dead isn’t instantly fatal for the group, making the tank the most important target to heal. Otherwise less heavily armored classes are probably more in need for heals than heavy armor classes, who can take more hits. Also melee classes tend to need more healing than ranged ones as they get hit by more of the mobs’ aoe attacks.
Healers also have skills to revive their defeated fellows. Some of these can also be used while in combat, but have long cooldowns.
Healers also have some utility skills - for example to reduce incoming damage or to boost fellowship’s damage. Learning to time these correctly can make a great difference in a fight.
Tank, healer and dps form what is often called a ‘holy trinity’ of mmos, the core roles of any group. In addition there are several more supportive roles:
Crowd Control (aka CC) - Crowd controlling is a secondary role that allows keeping mobs away from the group.
There are following different types of crowd control in game:
Conjunction stun (aka fellowship maneuver stun, knockdown) - Most powerful form of cc that completely incapacities the mob, making it unable to move or attack and interrupts any actions it was performing. It also allows the execution of a fellowship maneuver unless said mob is immune. Conjunction stun cannot be interrupted and results in a temporary stun immunity being applied to a mob for few seconds, during which it can’t be stunned again.
Stun is similar to conjunction stun, but it does not allow fellowship maneuver to be done. In addition many bosses are immune to regular stuns and any other of the following forms of cc.
Daze prevents the mob from moving or attacking. It lasts longer than stuns (typically 30 seconds), but it breaks if any damage is done to the dazed mob. Note that people often refer to daze as stun. For example a raid the leader might ask someone to ‘stun’ a mob when he actually wants it to be dazed. Daze is the most common form of cc used in organized crowd controlling.
Root prevents a mob from moving, but it can still use its attacks (ranged attacks or melee attacks if you walk close to it). Roots are broken by damage similar to dazes.
Fear prevents a mob from attacking and makes in run around in terror randomly. Also fears are broken by damage and a feared mob might call any nearby inactive mobs into battle if it’s close to them when the fear ends.
A slow (aka snare) simply slows mob’s run speed. Slow does not count for many cc related things like special buffs removed by cc.
In raids mobs often have some defense against cc. They can be totally immune to it, selectively immune (for example you can stun but not slow) or have some kind of cc shields. Common mechanics include double cc (you need to cc mob twice, first to remove anti cc shield, then to actually apply cc) and one time cc (you can cc mob once and it then becomes immune to the used form of cc or totally immune to cc). Most bosses are totally immune to any cc (with the possible exception of conjunction stuns).
Debuffing - Debuffing makes the mobs less dangerous
Debuffing means reducing the mobs ability to attack or weakening its defenses. Common debuffs that make a mob less dangerous do some of the following: reduce mob’s outgoing damage (specific by type: melee, ranged or tactical), reduce mob’s critical hit change, increase mobs attack duration and/or miss change. Debuffs that make a mob take more damage include: increased incoming damage, increased incoming critical hit change, reduced armor value, reduced avoidances.
Lore-master is the only class in game that can have Debuffing as primary role and even still he’s expected to some healing and damage in addition. Burglars also have several debuffs, but they use them in addition to dpsing.
For some boss fights debuffing is near essential for success due to bosses dealing huge amounts of damage. In other cases debuffing greatly lessens the stress on healers and increases changes of staying alive as whole group takes less damage and several critical hits from mobs in a row are less likely. Reduced mob defenses also make the fight go faster, making a debuffer valuable, although not necessarily essential addition to the group
Buffing - Buffing increases the abilities of your fellows
Buffing is secondary ability that makes the buffer and his fellows more powerful. Typical buffs boost primary stats, critical change, avoidances, defenses, damage or attack speed. Captain is the king of buffing, but also minstrels have several group buffs.
Buffing is supportive role and the buffer should also contribute to healing and/or damage in addition.