I'll start it off with (and this is pure protip for dps starting). Don't run ahead of the tank, even if you've done the dungeon plenty of times before...you will die, no one will heal you, and the tank is not going to follow you.

I feel like this one has stood the test of time, in all my years healing and tanking, it alwas happens. You get some gung-ho archer or lancer, run ahead and boom, dead, because they thought the team would follow them.

-Never ask for a recommendation....can't believe somebody would even....