How to assume a raid mentality

As I said in my last philosophy post, it is my opinion that the leveling process does not sufficiently help a player develop the mentality they will need to have when they start doing dungeons and raids. For those who wish to raid, 5-mans are usually the way to learn said mentality, and that's where players can practice their roles. Because players may not know how to approach their first 5-man run, I have decided to give a basic rundown of how a player should think about their roll in a run. Think of this as a teaching you the mentality you will need when you are in a group.

First of all, what are the roles that a player can fulfill in a raid or 5-man? A 5-man run is usually made up of a tank, 3 DPS (it stands for damage per second, but it means damager), and a healer. Here are the various classes and specs that can fulfill the three roles.

Tank: Any Death Knights (Frost is preferred, but as long as you are in frost presence and go for defensive talents, you should be all set) Feral Druids (spec'ed to improve bear form), Protection Paladins, and Protection Warriors.
DPS: Any Death Knights (Blood and Unholy are prefered, but as long as you take offensive talents and are in Blood or Unholy Presence, you will be ok), Balance or Feral Druids (Feral Druids will need to spec to improve cat form), any Hunters, any Mages, Retribution Paladins, Shadow Priests, any Rogues, Elemental or Enhancement Shamans, any Warlocks, and Arms of Fury Warriors.
Healer: Restoration Druids, Holy Paladins, Discipline or Holy Priests, and Restoration Shamans.

To describe the roles most simply, tanks take damage, DPS do damage, and healers heal damage. Tanking and healing are generally agreed to be more difficult roles than DPS'ing, as well as more consequential. I would say that tanking is most difficult, while healing is more consequential, but it's really a subjective thing. Considering that all classes can DPS, and that the armor you acquire while leveling can probably serve you as DPS armor, if you are completely new to grouping, it may be a good idea to start as a DPS before moving on to tanking or healing. That said, having some experience tanking and healing will definitely give you a better perspective on what your group-mates go through, so even if you don't think you can handle the roles, don't immediately think that they are beyond your reach. Many of the best DPS'ers I have played with have experience with tanking, as have some of the best healers.

Regardless of what role you take, there are certain ideas you should include in the mentality with which you approach raiding or 5-mans. These may seem like common-sense things to veteran players, but then again, so will most of the things in this post. If you haven't grouped with other people in WoW before for longer than it takes to complete a group quest, think of these rules as ways of thinking about grouping with other people.

-I will recognize that there are other people behind that characters I play with, and I will recognize that they also have goals and things they wish to accomplish with this run.
-I will use abilities I may not frequently use while solo-ing if they benefit the group.
-I will not use my solo-ing/PvP spec while in an instance, unless my spec contains all necessary talents for both grouping and solo-ing or PvP.
-I will not stand in any fire/black zones/"bad stuff" unless that is part of the boss strategy.
-If I have not run the instance before, I will say so and listen carefully to and follow all boss directions given to me.
-Better yet, I will read the boss strategies on wowhead or wowwiki beforehand so I only need a reminder when I go into the instance.
-I will not run an instance I am not prepared for, gear-wise or skill-wise.
-I will bring the reagents I need for my spells as well as any buff food if I need it.
-I will not distract myself by talking on the phone or browsing the web, unless we are waiting for someone to come back from being AFK.
-I will not go AFK unexpectedly, for longer than is reasonable (5 minutes, usually), too frequently, or in the middle of a fight. I will use the bathroom before the run and will limit myself to one bathroom break during the run.

Now that we've gotten those out of the way, let's look at the mentality you need for each role.

Tanks:
-I will be willing to lead the run, unless I have very little experience with instances.
-I will make sure that all of the mobs we are fighting are fighting me, not any of my group-mates, unless letting them attack someone else is part of a boss's strategy.
-I will focus on causing maximum threat per second, not damage per second. (This is not as much of an issue as it used to be, since damage is now more tied into threat than it used to be, but it's still important to keep in mind.)
-I will face enemies away from my group in case they have a frontal area-of-effect attack, like breathing fire.
-I will only use taunt when an enemy is not attacking me.
-I will always protect the healer.
-I will set the pace of the run to be fast enough that the group doesn't loose steam but slow enough to let the casters regenerate their mana.
-I will use a healing potion when I need to.
-I will move the enemy if he needs to be moved.

DPS:
-I will not cause more threat than the tank.
-I will cause maximum damage per second using the right talents, spell/ability rotation, etc.
-If the enemy attacks me, I will not interpret it as a sign that I am doing enough damage.
-If I can heal myself (through spells or bandages) I will do so if the healer needs to focus on healing the tank.
-I will recognize that I am the most replaceable member of the group and will thus do as much as possible to be a keeper, i.e. to motivate the group leader to not drop me.

Healer:
-I will not spend my precious time or mana casting offensive spells unless I and my group-mates far out-gear the instance.
-I will do everything in my power to not run out of mana.
-I will heal the tank and myself first, then the DPS, then any pets if I have extra mana.
-I will keep a watch on myself to make sure I don't take too much damage or stand in a compromising position (in some "bad stuff", in front of the tank, etc.)
-I will focus on endurance healing when healing during a boss battle.
-I will use my most mana-efficient heals and will avoid overhealing unless the tank is taking a lot of damage and could die if I don't pump out the maximum healing possible.
-I will bring water to each run to regenerate my mana, in case there is not a mage to conjure food.

That about does it. As I said, if you have experience grouping with other players, then there will probably be nothing new in this post for you. This is simply a guide to how you should approach the prospect of grouping with other people and fulfilling your role well. If there are any important things that I missed, let me know so that I may make a more complete list.