One thing I highly recommend is having party battle effects set to limited, and focus your attention on the boss during a fight. The animations can tell you a lot about who got hit, and if you have overhead health bars you can see the tank's HP as well (as they should be right next to it). You only really need to look at the party list when you see an AoE go off, and I'll actually usually toss out my own AoE heal in response to their AoE attack, THEN look at the party bar to see if I need to deal with debuffs or toss out a second one. Likewise if you see them charge up for a bit and then do a beefy looking hit on the tank, toss them an equally beefy heal on reflex.