Eat about 1-2 hrs beforehand and drink plenty of water. Low blood sugar and dehydration will make you feel ill quickly.
Open all the vents...get lots of fresh air.
Fly as much as possible yourself, much less likely to feel ill if you do the flying.
Tighten the lap belts as much as possible and don't overtighten the shoulder straps.
Stop if you start to feel ill and land. You won't 'recover' while flying.
Very few people feel ill, especially if the pilot/instructor is a good one.
Enjoy it!
ZA
ps Bananas are good before the flight... they give you blood sugar and also taste the same on the way down and the way back up!!!!