Even though I'm a warrior, I love when BLMs use sleep instead of spamming fire2 and flare. It makes both my job easier aswell as the healers, plus I wont have to drain my TP to hold aggro (yes, overpower costs alot of TP). I can just imagine the dread of being a pally when it comes to BLM, SMN and BRD pulling heavy AoE damage.

And if you do get aggro as a dpser, run up to your tank and stop dpsing for a moment so he can build enmity. Thats what the aggro meter is for, green = dps like a maniac until you drop, red = stop dpsing please.
And if you're a healer, never cast a spell on the tank as he pulls, you will get aggro. Overhealing is also bad.