In a snippet from this article on BBC News, they provide some sounds advice:

“The brace position is a position that will offer you the best chance to survive in a crash because it stops you from flying forward and striking the seat or interior in front of you,” says Mr Barth.

“The important thing is to get your upper torso down as much as possible, limiting the ‘jackknife’ effect from impact forces.”

That said, here’s something that should give you a little comfort if your fear of flying goes beyond a lack of understanding aeronautics:

In the US alone, between 1983 and 2000, there were 568 plane crashes. Out of the collective 53,487 people onboard, 51,207 survived.

The article also highlights a television show that premiers tonight:
Horizon: Survivors Guide to Plane Crashes is on BBC Two at 2100 BST on Tuesday 3 October. Watch video highlights at Horizon’s website.

Hopefully you’ll never have to use this information, but at least it should make your next flying experience a less anxiety ridden one.

Happy travels!