How long is the flight? Some flights have the anti-anxiety films or audios to listen to, these may help.
Someone has told me that antihistamines can help you to relax on the flight... I am going to try next time :)
I absolutely get petrified before flights. I try to make sure I get plenty of sleep before flight and have some lemon balm or chamomile tea, it may not take the anxiety away but helps to cope with it a bit better.