Just to answer the origional question, when I'm at the field, and a beginner's plane is up in the air, and going to one side, here is what I do so we can get some training done.

I get the plane straight and level, then go hands-off. If I think I see a yaw-then-roll, I trim more rudder, if I see more roll-then-yaw, I trim ailerons. If I'm not sure, I frequently split the difference and just do a little of both.

The way I see it, I've got about 15min of fuel on board. The more time I spend messing with the trims, the less time the student is learning to fly. And we only have so much daylight during a day or evening at the field, so the less time we spend with the airplane taken apart, the more time the student is spending learning to fly.

Once the student learns how to loop and roll and fly basic acrobatics, we can talk about ways to trim for better acrobatics.