You're right, more exposure will decrease the chance of air sickness. Remember Chuck Yeager got airsick when he was learning to fly. So did I but I am no where near as good as him.
Pick your days. If it's blowing a gale then it'll obviously be rough and not good for calming jittery stomachs. A cooler day is wise too.
Drink water, don't consume any thing that might upset your stomach. Definitely don't fly with a hangover.