selm

This sounds silly at first, but believe me, it works. Look at yourself in a mirror, smile and say to yourself: I like you, I LIKE you, I like YOU, I love you. After you giggle the first few times, it makes you feel good inside and better prepared to face the world with confidence. The best part is you'll really start believing and feeling what you're saying. You certainly deserve to love yourself.
Another way to gain confidence is to "act as if". Before you head into a stressfull situation, visualize yourself handling this situtation with confidence. Then, when you actually enter the situation you'll be better prepared to be confident.