In my experience it's blind guesswork. I'd love to be proved wrong.
What I have done with most of the aircraft panels I make is to always include an elevator trim gauge, so that you can see the result of the trim input you are making. Most of my stuff has been with Jets on the FOX-FOUR Korean Air War site, so elevator trim is really your main concern.
We're now doing an A-26 Invader Campaign, so I've put Aileron and rudder gauges on my panels for that one. I believe I did the same with the Sea Fury.
These gauges are available, and it's fairly easy to install them in any Panel. If you're having trouble doing that on your favourite aircraft, then just download a FOX-FOUR aircraft and steal our gauges.
We're here:
http://www.simviation.com/lair/cfs2korea.htm