For the Mini-Bosses/Bosses: ALWAYS pop Fight or Flight before attacking, the extra damage helps with your enemity. Flash against single targets is a no go beyond blind, 2-3 maybe 1-2 before jusy cycling through with your Halone combo, anything more Flash will be used more often. For your definsive CDs use this time to learn how each work with you and all that. Its mostly end game fights where it really matters and by then you should either have enough of a feel for them to know what to use once you know the fight a bit, or can ask a buddy who also tanks.

Also CoH ftw.