The first rule of self-confidence that I have developed for myself comes from one of my favorite quotes:
"We are what we believe we are." - C.S. Lewis
You may think of yourself as the most shy, introverted, insecure person there could ever be. The idea of believing you are confident may seem unfathomable. But I cannot stress enough the importance of believing in yourself! Have you heard people say "fake it until you make it?" That is basically what I am saying, but I don't really like the "fake it" part because I would never encourage anyone to be fake. Just be yourself and believe in yourself even if it doesn't feel exactly right at first. Because with time it will feel right and you will BE confident!