Psycoloical viewpoint: Confidence is aqquired from success of achievement. So, set yourself realistic targets. When you accomplish them, you will, naturally, feel more confident. Try new things, stretch yourself, but not so that you set yourself up to fail. There is no way you can suddenly become confident over night, although I agree with the post that suggested you learn to love yourself.
Saying things out loud is very good for helping yourself. For example, when something makes you laugh, you can say, to yourself, (after all, we don't want to get locked up!), "I enjoy how my sense of humour makes me laugh". Or, if you are talented in a particulr way, say, gymnastics, "I love how I have learned to strectch myself this far". Society these days teaches us that it is a crime to appreciate ourselves. It is not. How can we be confident if we shy away from our achievements?
I don't doubt that you possess wonderful qualities. The trick is, that you see them for yourself. When you can see them, affirm them with conviction to yourself. Good luck! :D