If you keep an eye on the mobs emnity status, and you're main using f2/flare, swap targets to a green one when you see your target going yellow. Sometimes in DF you have to adjust to the tank rather than all-out DPS. some can handle whatever you throw at them, some it's better not to buff during trash... and some can't even manage a flare...

if you do aggro something, use manawall/ward to assist the healer.