When I started commuting, I observed and sometimes copied other cyclists. This was interesting and a good way to learn the shortest and most efficient routes. After that, though, I made a pact with myself to ignore others and stay in my own zone. This does require developing a thicker skin, but ultimately I think it's made me a more confident and safer cyclist.

Not a day goes by that I'm not sitting at a stoplight when someone whizzes past from behind. Being raced on the Manhattan Bridge is an everyday event. I admit there's an occasional voice in my head saying, "Good for you, Twenty-Something on a Road Bike, you can smoke a 52 year-old woman on a hybrid." But mostly I'm just enjoying my ride on my own terms and thinking it's my life and no one else's. So I agree with the above that the only instinct you should heed is your own.

This is not to say that you should never challenge and overcome your fears, but in my experience this comes naturally over time.