think about all your positive attributes, and always remember them. in EVERY situation. there is no reason for anyone to not feel confident in themselves. the only person you should allow to judge you is yourself. so look at all the good things! and eventually when you gain more confidence, address the "not-so-good" things. in being more confident already, you should have no problem tackling thos issues head on now!
Go to drama classes, I did and they help a lot (:
hope i helped!
Change your appearance
Pray and believe in what you asking for that's the best way to improve Self confidence
Picture everyone in their underwear, obviously.