When you book your reservations, ask for seats over the wing. These seats offer the most stable ride in the whole airplane. It will help guard against the motion that causes airsickness.
Had motion sickness before? See your doctor ahead of time. There are patches and there are several kinds of pills. Know that the ones that work the best may render you too sleepy to be any good for the day, though. If you're going to be in the plane a long time, like for an overseas flight, the strongest ones may be the best. He can also give you a patch and some pills together. The over the counter ones are not very good for those who have serious problems, so see the doctor.
Wear loose comfortable clothing on the plane. Things that are tight around your tummy or chest are going to worsen feelings of nausea. Wear something really loose and comfy and having a couple of thin layers will help you to be cool enough. There are thin blankets if you're cold but if you're usually hot, you need to dress in breathable (cotton) clothing.
Eat foods that are light and easy to digest before you fly. This is not the time for an 6-course meal. In the morning, scrambled eggs, toast and coffee is plenty. Later on, try soup and salad or a baked potato and plain small steak. Go easy on the spicy and greasy foods like tamales or bacon and avoid really heavy foods like lasagna. It's hard to digest all that when you're sitting down for hours after you eat.
Alcohol and cigarettes both help to make motion sickness worse. Try not smoking for a few hours before you go and leaving the drinks alone before and during your flight.
Bring some plain saltine crackers and get a clear soft drink while on the plane. Avoid coffee, but you can sip a little hot tea which helps to settle the stomach down. Bring a couple of peppermints, but only eat them if you feel sick. Putting anything in your mouth will get your stomach juices flowing so don't chew gum or suck on candy through the trip. You can also try powdered ginger capsules (available at health food stores). Take two about 20 minutes before your trip and then while on the plane. Some people find that cinnamon helps but again, only do this after you feel ill.
After you're in the plane, let the air blow directly into your face. Make sure your clothes are loose and you can unbutton or unhook things and cover it up while sitting down if that helps. If you feel any nausea, lie back and close your eyes or focus on a fixed point in the plane. When you see things that are still-looking and yet you feel movement it throws off your equilibrium, so closing your eyes or focusing them on one still object can help the body to adjust to the discrepancy between what it feels and what it sees. Deep breathing through your mouth will also help to quiet your body systems down a bit.
Taking some precautions before you go on vacation can ensure that you can enjoy every day that you have. After you do these things, all you have to remember is to have fun.