Here are a couple of things I do -
1) Turn on the air vent full force and aim it directly at your face. Oxygen is one of the best antidotes for air sickness.
2) If there is good visibility out the window, look as far away as possible and fix on a specific site. When that site disappears, find another one. Watching things go by makes things much worse. This is what skaters and dancers do when they spin.