A little bit of self belief goes a long way. Turn those chattering thoughts into something positive, just go for it. Its amazing how the mind plays tricks on us and can eventually stop us from progressing forward, experiencing new things and enjoying life.
What ever you feel you want to do, take steps towards achieving it. No matter how small!
Don't let anyone tell you otherwise, other people have a fantastic way of letting their perceptions dampen your drive and excitement. Prove them otherwise.
Push yourself out of your comfort zone, you never know how you will feel about it. It could be terrible (whats the worst that can happen) It could feel AMAZING!
Most of all, don't let that self doubt creep in. Believe in yourself.