I thoroughly enjoy being a mage.  I've been one since Old World and raided one since Molten Core, when Frost was the COOL SPEC.  I've done all sorts of instances and can honestly say I've used just about every skill on my bar at one time or another, aside from the fire spec skills that I've never delved deeply into.  Unlike some classes, we're no hybrid.  Mages have their own little safe niche of DPS that we never stray from, we rarely change specs, and never need to adjust that role.  While I love what I do, there's always been that nagging voice in the back of my mind telling me that I need to understand the other roles in the group too.  And I have done my share of both of them.  So from a mage's perspective as well as the view of these other two types of people, here's the wisdom I've come up with.

Tanks

This is the person keeping you from dying by holding agro on all those evil people you're pewpewing.  He's the meat shield, the wall behind which you hide.  We can make their jobs very difficult and they can do the same for us.  A tank without much threat is going to lose agro and generally, with arcane mages anyway, all that hate is pouring right into your squishy cloth lap.  We have those lovely defensive cooldowns (Mirror Image, Invisibility, and Ice Block), but they're not always up and you can't really chain cast them.  There's also the option of cutting back your DPS or stopping completely, but no one likes that, because let's face it.  Mages are meter junkies.  (Don't lie.  You know you are.)  We live to give the other DPS a run for their money on that damage bar, to prove that we're capable and that we're holding up our end of the bargin.

But here's the thing:  if you're pulling agro often, you're not holding up your end of the bargin.  ESPECIALLY in pugs, you don't know what kind of tank you're gonna get.  I've been randomed into some brand new groups on all my characters, being the person with the top gear and the most experience.  Sometimes the person with the shield icon has just queued under tank for the first time and while he or she hopefully has some idea which buttons to press, they're going to sweat it.  If you make their job harder, not only does it hurt the group and prolong your time spent in it, it makes you one of those people that gets blacklisted to ignore lists. 

I have an 80 DK tank who I've raid tanked on as well as taken through heroics with both PUGs and people I know.  I've dealt with mages who didn't know how to back off if I was struggling and also with some mages I loved grouping with.  A lot of tanks view DPS as replaceable and most of them won't hesitate to /votekick your ass if they think you're being a jerk; I've done that before.  I've also stopped to give mages some suggestions on how to help their apparent issues.

So how do you help out your tank? 

• First of all, stop staring at your meter.  This is a tool for you to use to assess your PERSONAL performance and tweek your spec or rotation.  Not to blow all your cooldowns in a tight spot and see if you can beat your personal best dps lol.  If not the meter then how do you assess how you're doing?  Are the mobs staying up a particularly long time?  Are a lot of other people hitting something you're not hitting?  Is your tank doing the pulling?
• Don't be an asshat and pull for your tank.  The only DPS class that has even the vaguest business pulling for a tank is a hunter with misdirect and since they don't give that to mages, don't pull.  If you're CCing in a pull, do it after the tank has agro on the other mobs or when you're sure they can pick them up off you.  Otherwise you will die, and we won't feel sorry for you.
• You're not melee.  So don't be in melee range.  It's a lot harder for a tank to tell if they've lost agro on something if you're standing on top of them.  Most good tanks run threat meters (which is a great idea for DPS too!) but most meters can only tell you about a single targeted mob.  Some fights require you be in melee range, and those are excusable, but otherwise, don't.
• If you get agro, use your cooldowns.  Frost nova does not count as a defensive cooldown, by the way.  It's a pain in the ass for a tank unless you know how to use it correctly.  FNing a mob on the other side of the room from the tank makes it hard for the tank to resume agro on that mob as all tanks (currently) are melee tanks.  Your defensive cooldowns are Mirror Image for threat distribution between your mirrors, Invisibility for a complete wipe, and Iceblock for some invulnerability and time for the tank to pick up agro again.  There's no reason to use them all at once or even two at once.  Just use them wisely.  Also, if you get agro, don't freak out and start running around like a decapitated chicken.  If all your cooldowns are unattainable, then take the mob back to the tank and frost nova it right next to him.  That is the only way to use it right in a group as far as I'm concerned.

Healers

Unless you're an alchemist or REALLY talented with bandages, mages do not have true heal spells available to them.  In this case, we're dependent on the healer(s) in the group to fix our falling HP bar.    There's any number of ways you can screw this up for that player; standing in fire, attempting to tank, falling off cliffs...  In any case, this person is not here to personally heal you.  DPS do not get pocket healers.  The reason these people are here is to keep everyone at their optimum level of health and their primary target is not their mage, but their tank.  Generally the plate monkeys should be the ones taking all the damage anyway, so don't be surprised if they're the ones getting all the heals.

I played a raiding discipline priest in old world and have been leveling a Resto/Elemental shaman.  I also at one point played a multi-tasking druid (before dual-speccing I might add.)  I've been behind the healer screen a good bit and it's not my favorite thing, but it's given me a better understanding about how DPS can screw up my day.  It probably doesn't help that I'm spoiled with a number of good guild healers who regularly put up with shit from the DPS, but I'd like to think I've seen their perspective on things.

So how do you help out your healer?

• Use your consumables.  If you have food, eat it.  That extra stamina will give you a slightly larger health pool and a little bit more time for the healer to throw a heal or a shield at you to keep you dying.  Let's not forget our other consumables too:  bandages, potions, and healthstones.  These are not sparkly trinkets to rot in your bags till you need them soloing.  They are also there for grouping.  If your group is between mob packs, sit down and eat some strudel.  A little munching never hurt anyone and in WoW you can't overeat.
• Summon that Strudel!  Healers love this stuff.  It makes their mana go up when it's low and they have time and they don't have to use their own bought stock which can get expensive.  Plus if you put down a table, it saves them for a number of groups besides your own.  They will love you from the start if you just throw down that table.  It only costs you a few Arcane Powder which is super cheap in the WOTLK economy.
• Cooldowns again!  If you find yourself pulling agro, use your buttons!  If the healer can go back to the tank because you're no longer losing health, this is a good thing.  Even mana shield and polymorph help in this situation.
• Buff up!  While most tanks could care less about Arcane Intellect, healers usually love it because extra mana = extra heals before Oom!  I also end up tossing my healer Focus Magic when there's no other caster DPS and sometimes when there is - a holy paladin usually stacks a heck of a lot more crit than a number of other classes.  Even amplify magic has it's place in an all physical damage fight like Deathbringer Saurfang.
• Be nice to your tank because by proxy, you're being nice to your healer.

Let us not forget the etiquette of being a part of any group as mentioned in one of my previous posts about raiding and PUGs.  It always makes it less stressful for your group when everyone knows how to play nice.