This is a half rant, half silly page describing how not to act in an instance, and some of the things I've seen people doing in instances. (this is a sarcastuic thread, for anyone who wanders here by accident looking for actual articles about how to work together in instances.)
General Tips for InstancesEdit
In general, think of an instance like a space invaders type of game: your job is to shoot down all the aliens, equivalent in World of Warcraft to enemy monsters. it is even better than space invaders, actually, as if you die, you can simply run back to the instance entrance, instead of loosing the game and needing to start over. Many players in the game make the mistake of moving slowly through instances, assuming that they need to use things like "crowd control" or "pulling" to get through the instance well. They perhaps are new to the game, or have been reading too many guides written by unskilled people, as the best way to get through an instance is definitely to attack as many enemies at once, and focus purely on dealing damage quickly to them.
Most players have little sense of how an instance is supposed to work, and will assume that a "tank" or "healer" is needed, thus, all players are unfortunately expected to provide room in instance groups for character with tanking or healing skills. You will simply have to accept this grouping for the time being, than play the correct way when you enter the instance.
If you are playing a warrior, Paladin, or Druid, you are a character with "tank" skills, and might be expected to try to tank. Similarly, if you are playing a druid, paladin, shaman, or priest, you may be expected to use "healing" skills. "Tanking" does involve dealing damage, so you can satisfy less experienced players while performing your actual role of dealing as much damage as possible. When expected to heal, reminding people that you aren't speeced for healing works fine for avoiding having ot waste mana. Some people may argue something like "But you are the only character that can heal". They are inexperienced and should just be reminded again of your spec.
(This actually happens a surprising amount, where I will be in a group with, say, a warrior, paladin, warlock, hunter, and mage, one person will say something like "It looks like the paladin is healing", and the paladinwill say "I'm not specced for it", without apparently realizing that there is no one else in the group who can heal at all.)
Blizzard has also introduced an unusual combination of features: They have included meeting stones to allow two people to summon everyone else to the instance, but anyone who actually helps summon others to a meeting stone will loose a lot of the instance loot. It is thus important to not be one of the two people who first go to the meeting stone, asking for a summon, or mentioning that you are too far away, will encourage other people to go to the meeting stone first, keeping your loot safe. Even if you are the closest or fastest person to the meeting stone, saying these expressions will encourage more impatient people to go to the stone instead, once again leaving you with your loot intact.
Inside the InstanceEdit
Generally, groups prefer not to start over, so if you are inside the instance, you are free to play the most effective way, rather than trying to fit in with the "tank/nuke/heal" type of gameplay preferred by others. At this point ,whatever your usual role, you should simply use your DPS talents and skills to deal as much damage as quickly to monsters as you possibly can. If the healer complains of difficulty healing, or the tank or any other members complain that you are "pulling too much aggro", "breaking crowd control", "aggroing too many", etc., simply ignore them, as they are less experienced an do not understand how to correctly play an instance. Remember at all times; world of Warcraft=Space Invaders.
In fact, reading team chat is a bad idea in general. Reading team chat slows you down, and can cause eye damage when you try to focus on the small writing on the corner of the screen. It is much more efficient to simply keep attacking using your direct damage skills.
If party members mention that they are 'out of mana" simply ignore them, as they are keeping you from finishing the instance. However, make sure to warn other members of you party that you are out of mana, you wouldn't want to be left behind and out of loot would you.
If enemies run away, it allows you to finish the instance faster by bringing other enemies to you rather than forcing you to go to them, simply attack on a different enemy when one runs away to keep your DPS as high as possible.
Sometimes, to follow the space invaders analogy, the aliens will reach the surface and you will have to recover your corpse inside the instance. Generally, this is the fault of the healer, who often runs his/her mana out using healing skills, rather than DPSing as they should be doing. Make this known to the healer, as you would not want to cause other groups to wipe for the same reason with this party member in the group.
Healers do often have useful resurrection skills, so you should simply wait for the healer to reenter the instance and resurrect you. If there are respawns in the instance, it gives the healer an opportunity to practice their true role in the instance, you should leave them to discover this on their own, rather than dying and going back to the beginning to assist them, which will cost you valuable repair bills.
Hunters especially have an advantage with wipes, as they can feign death to save repair bills. Other members of the instance might complain that they are going too slowly without the hunters help, but you should ignore them, as they obviously weren't playing right and need to be taught to deal damage quickly, rather than wasting time with whatever they were doing when the wipe happened.
Class specific tipsEdit
Warrior: You want to be specced fury or arms. Whether "tanking" or not, you should simply pick one enemy at a time and attack them with either your duel wielded weapons or a good two-hander. Always keep your rage bar full, with each point of rage saved up, your damage increases by 1%, which adds up heavily for full rage.
Paladin: Spec Retribution. Whatever anyone says, you will be DPSing, so use seals oriented towards this task. go with retribution or Sanctity aura, even if another Paladin has that aura up already, as you may get separated and need to have it yourself.
Priest: Party members will fortunately expect you to be shadow for leveling, so that issue is taken care of already. Priests are often expected to heal, so you will want to throw out heals occasionally to keep party members happy, but otherwise use shadow damage skills, and holy fire, as much as possible. If party members complain that you are "wasting your mana", or 'should be healing, not damaging", mention that you are shadow specced, and that should keep them off.
Druid: Druids unfortunately cannot heal while in their damage form, (cat form), so you will just have to remain in humanoid form and use balance spells to help out in damage dealing as much as you can. Some parties will let you use your best spec of feral, but expect you to go bear form to "tank". Bear form fortunately can deal relatively good damage, so stick with that form and play it much like a warrior, described above.
Shaman: Shamans, like all healing classes, might be expected to heal, but fortunately do not have to do this as much as priests or druids usually do. Casting totems wastes time and should be avoided, except for cool totems like windfury, otherwise, simply attack. Enhancement or elemental are the best specs for a shaman.
Mage: Mages are fortunately expected to simply DPS anyway, so just blast away. If you draw aggro and die, remember that it was the healer's fault for trying to heal you instead of DPSing like they should.
Warlock: Similar to mages, warlocks are simply assumed to be DPS classes, so you may simply blast away with your spells. some people will expect warlocks to use "utility" spells like soulstone or healthstone, these take a small amount of time to cast, so feel free to use these abilities to keep others happy. Your pet doesn't really matter, unless you have a felguard, so walk in with whichever demon you find cool or happen to have out, unless you have the felguard spell, in which case use the felguard for its large size and cool look.
Hunter: Contrary to popular belief, hunters can melee as effectively as any melee classes, so feel free to either do ranged or melee damage as suits your fancy. All talent specs are worthwhile, but with beast mastery you can show off a high damage pet. Hunters count for two people, thanks to their pets, so having a group of 3 hunters is better than any 5 character instance group made of other classes.
Rogue; Rogues are cool because they can stealth, which allows them to walk among monsters without fear of annoying their teammates with aggro. Rogues are just expected to DPS usually, so you have nothing to worry about in this area.
Instance Tips for Particular InstancesEdit
Blackfathom Deeps Many groups do not like to activate all the summoning bowls at the same time, but opening them all at the same time gives everyone in the party a 200 DPS sword, so feel free to activate all bowls when the room has been cleared.
Stormwind Stockades The stockades is an excellent instances for constant killing, as there are a lot of enemies packed closely together than run away.
Gnomeregan Later in gnomeregan, there are groups of enemies that drop bombs. Do not worry, these are just like weapon aliens will use in space invaders, you can simply dodge these bombs and focus on the aliens. Gnomeregan was also the first instance designed, and as such it fits closest to the "shoot down aliens" gameplay originally envisioned by blizzard.
Scarlet monastery It can sometimes be difficult to decide which instance in the monastery to go to, as each group that enters has a chance to win a 300 DPS two-handed ax, so you may need to switch instances from the one originally planned.
Scarlet monastery is also a long trip for the alliance, making it much harder to convince other people to be the ones to go to the meeting stone,as no one likes to run a long way. If you are a shaman or druid, you will want to skip this instance if alliance, or at least be in kalimdor, otherwise other party members will expect you to travel there.