#1 when you find mobs let the tanks TANK, do not immediately launch a fireball or shadow bolt into the mobs. Let the tanks grab aggro and have at least 8 seconds to build aggro before you start with the fireworks. I can't count how many times I have been in a party (as a warrior) and as soon as we see mobs the mage starts a fireball, and my warrior is left chasing a mob trying to get it off the squishy.

#2 when you draw aggro, RUN TOWARD THE TANK! You probably can't get away from the mob very easily but you probably CAN get away from the tank, and you DON'T want to get away from the tank.

#3 if your healing, HEAL don't use mana for anything except heals. I know I want to do a little damage when I am playing my priest and I often have to tell myself "it's not your job to kill the mob!"

#4 put away your pets! Only bring them out for boss encounters. I've seen many a rogue pet run away and bring back half the dungeon. And worse I'm not certain why this happens, that's why pets scare me in instances.

#5. Good DPS classes don't just unload, they manage their hate by slowing down a little. That's time to use your wands, unload 2 to 4 nukes and then start using your wand.

#6 Even if your not the tank, its your job to protect the rezzers, if a priest is getting hit you can ignore #5 and just unload with everything on the mob that is hitting the priest.

#7 /assist, learn how to use it, learn to love it and make a macro out of it.

/assist

#8 Keep an eye out for runners.


And For Tanks

#1 two handed weapons and dual wielding are great but carry a shield. Sometimes you just need to be able to take hits and you'll make the healers mana last longer.

#2 carry heal potions and know how to make and use a bandage. If you can find other things to heal you keep them around.

#3 Sunder (and Rend if possible) everything in sight and hamstring mobs that can run away. Throw in a thunder clap if you can.

#4 Pallys, try and save your stun for runners or when a mob goes after a squishy.