A lot of the position things I learn in chorus actually help me envision how I should be riding.
They always tell me to pull from the top of your head to stand tall. When I do this riding I always pick myself up out of my seat (not good!) so I just imagine it a little.
In addition, they tell me to relax in chorus, which helps my position in riding. When I get stressed, I lean forward, I lock my elbows, and my legs go nearly up to the cantle. Just an exaggeration, haha.
I also find that working out to strengthen your arms (forearms included) back, LEGS, and stomach really help a lot.