I had the same problem when I started riding. I'd get nervous before each ride. I read this book, which is not at all cycling related:

http://www.amazon.com/Creative-Habit.../dp/0743235266

Tharp's approach to doing anything creative is to make it a routine, like brushing your teeth. This has worked well for me with many things, but especially cycling. On days I'm going to ride, I dress, pump my tires, brush my teeth, and get on the bike. No hesitation allowed. You can come up with a million reasons not to ride if you let yourself. Fear is just one of them.