I find that the more one understands about flying the better:

What is turbulence? Is it dangerous? How does the plane stay up in the air? etc. etc.

A lot of this can be answered by buying a textbook on flying - but one thing I recommend to most fearful flyers is that they call a local flying school and ask to sign up for a few hours of private ground school. Ask them to take you through some of those questions, and once you learn the factual information behind turbulence, etc. I think it will diminish your fears.

There are also a few books out there for fearful flyers, so you might want to check those out, too.