Damage dealing classes are the most populous of characters, so I figure a lot of you here are going to be picking those ones.
I got some great advice for tanking here, and have made a lot of progress because of it so now I want to return the favour.
Please bear in mind this isn't advice for what skills to use or anything exclusively class related so much as it is advice for how best to compliment your healer and your tank.
A consistent problem I run into is damage dealers trying to pressure the tank into moving forward, or not following the cue of the tank, for example:
* Not attacking in the marked order.
* Moving into new areas before the tank has (and often accidentally pulling mobs).
* Not giving the tank enough time to aggro. (One shield lob does not draw enough aggro to control an entire mob.)
* Breaking rank to retrieve a monster that's gone after the healer (that is the tank's job to deal with, focus on the monsters you're already about to kill).
I met some great people during Haukke Manor and Brayflox's Longstop who deferred to me (the tank) about what they'd like to do. If you want to explore everything and kill every mob for the experience, say something! Asking is never a bad thing and it helps the tank facilitate that. If the party seems unsure of a direction to go, offer one up as well, we're a team afterall.
On the note of healers, DDs seem to expect the healer to just keep them all alive without problems, but there are some occasions where you really should consult the healer. For example:
* Titan. His big ugly high in the sky attack does large chunks of damage to everyone in the party. Follow the tank or the healer (the healer will probably follow the tank). This allows the healer to do a quick AOE heal rather than waste the mana healing each person individually when they split to four corners of the room.
On the whole though, if you are unsure, or want to confirm (which you should) chat to the healer before a big fight starts. In most dungeons the tank's role is pretty straight-forward once they have the skills together to manage them, but the healer's role can be particularly taxing, and if it's a long fight their mana can suffer if every effort isn't efficient. A healer without mana is a bit useless, yanno?
Beyond that damage dealers need to be aware of their surroundings. As you move up in levels the dungeon bosses will start to do things like raise lamps in Haukke Manor and use bubble cages (Brayflox) and granite cages (Titan). These need to be taken down immediately. As do mob adds. The tank will often have to stick on the boss, because if they run around trying to help people with a problem that's easy picking they'll wind up cleaving the party. Mobs themselves are a bit different though. Discuss tact with your teams when you start.
All I'm really getting at here is that there are a number of small things that make a run much smoother, and communicating is key. Even if one or two people cannot respond for whatever reason, they can read the text and will know to take the cue.
The final thing I want to say is that there is a consistent issue with negative comments when people get frustrated. This helps no one. If you're bashing your healer because they're having trouble, all you're doing is being a spoil-sport and making that person feel worse, and often less inclined to be a team player. Likewise for the tank, and likewise for damage dealers. There's no reason to say someone sucks, or bash them, or be snarky, or make underhanded comments at them. You're not funny. You're not helping. You're not being a team player.
There are better ways, like offering encouraging advice. It isn't hard to do.
I have a strict rule: If someone behaves that way I abandon the instance / leave the duty. I won't play with people like that and neither should you feel obligated to.