Do you remember which boss it was that killed you? The reason i ask, is that most dungeon bosses telegraph their avoidable attacks. So you might not have actually been killed by an "invisible AoE", and it might have been a normal roomwide attack that the healer was supposed to get you through. Yes, you want to avoid the attacks you can to save your healer some stress but it is ultimately their job to keep you standing because almost every boss has a few moves that hit everyone and not everyone has a self-heal to survive it. As for general tips, pull your view out a bit to improve your overall vision. Certain bosses use physical tells to show upcoming moves, so watch for patterns to pick up on them(boss is raising a claw in a certain direction? probly about to do a big move that way so stand behind or on his other side). You can usually see boss adds appear on the aggro list to give you an idea of when they appear. And again, during bosses it normally doesnt matter if the tank switches targets. If there are adds that need to be killed, you just do it(whether the tank grabs them or not). If there are two targets, the tank is usually supposed to get aggro on both so you can keep targeting the one youre on unless theres an actual reason to switch. An awake tank shouldnt lose aggro to you if he has to hit something else for a bit. During trash pulls this matters even less, as you want to be using your AoE attacks most of the time. If something does peel off and chase after you, just stand next to the tank and he should get it back with his next AoE attack(and you would still be able to reach everything, so your AoE would still be fine too).

These are all general tips. If you know the specific boss, im sure someone here(if not me) knows the moves it does.

Bonus tip: You might already know this as a healer, but ill share for any other new players who might read this. When you get ressed during a fight you get a buff that lasts for a few seconds that makes you immune to most attacks. This buff goes away instantly if you use any attacks, skills, or spells. So when you stand back up from a res dont attack right away. Give the healer a chance to top you off(or use a self heal) and just make sure the boss isnt in the process of using a big attack that will knock you right back down again.