how to trim properly

[Bolelas]

I had never thaught of that mr Galway, and of couse it afects shooting! Thx for the post, and thanks also to mr Icefire. So, if ball is centred it should be ok, if ball centred and it is still roling we should aply aileron trim, correct?
Of course that for each engine rotacion, pitch angle, airspeed etc, the trim should change, so what do we adjust before combat? Or we must change also rudder trim in combat, just as we do to the elevator? (well... just use pedals to correct and shut up!)