If combat erupts and I'm not around to do it, I will activate searing flesh (1) as soon as I'm able to do so. It's an immediate action, but if I'm flat-footed, obviously it'll have to wait until my turn.
Don't risk attacks of opportunity while gathering power or blasting. Avoid gathering power over multiple rounds where there are archers or other dangers.
Move to avoid cover, then take ranged attacks. If fire immunity is apparent, move in, provide flank where possible (moving tactically, and without risking AoO), and use the dagger to aid someone's attack.