I used to feel strong motion sickness when flying aerobatics. I got to the point I could burn off the acro tanks in an Extra 300 without getting sick. I did 3 things:
Repeatedly spinning in an office chair until I felt dizzy then getting up and walking.
Flying as much as I could, and when I did, I would fly until I felt sick, then fly straight and level until I felt a bit better, then would do an avalanche maneuver (snap-roll at the top of a loop), then would fly straight and level again... and do it again, gradually pushing myself.
If you're in a car and not driving, try reading until you start feeling sick.
Somehow I never threw up flying aerobatics, but I did come really close a number of times.
I tried to relax, control my breathing, bring a little water with me, and always push myself a bit. And somehow that worked for me. Also if you do some aggressive maneuvers like lomcevakslomcováks, long tail slides, push humpty-bumps, and accelerated spins, most other maneuvers will seem much more tame and you'll be able to relax and enjoy them.
Good luck and have fun!