Relax. Enjoy the experience. I learned a long time ago there is not much point in worrying about something that is out of your control anyway. Keep in mind it is still the safest way to travel long distances.
Don't over medicate. I think that might just mess you up. Alcohol is fine if it helps to relax you...unless you are a bad drunk.
One thing I would suggest is some gum. I remember my first flight what bugged me the most was the ear-popping. You want to be chewing on something.
I'm not a huge fan of heights either, but for some reason, flying never bothered me. Again, don't miss out on the experience by worrying about it too much.