As usual, Cynfael speaks much sense

The DO NOT PANIC advice is probably the best advice you will ever get about T13. It is quite hard not to panic when you are starting out with T13 though, haha.

When my static were comfortable with mechanics, I was DPSing for all of P1, 2 and 3 except for Megaflare preparation, Flatten preparation and non-melee earthshakers. I healed more in P4 due to the sheer number of mechanics that occurred at the same time and the damage the tanks take, but as soon as the 4th Ahk Morn appears I switch back to full DPS for the rest of the fight.

The other thing I would say is to pick a strategy and places to stand/stack for each phase and stick with it.