I hate flying, and got really bad when i was doing 7 or 9 hour flights every month. I think the important things are to relax, and if that involves taking drugs then do it (I loved over-the-counter diazepam from chemists in India, but if you can get a doctor to proscribe it that's probably better!).
Make sure you are wearing comfy clothes...PJ's if necessary..and I always get an aisle seat so I can stretch my legs if I need to. Keeping fluids up is good, and I really like what Kittenfish said about turbulence, that is great advice.
Other than that, bring a book, a little pillow and a blanket if you can, and just pretend you're on a train.
Vicky