First you have to realize that you are #1 and forget what others do, say, dress and look. You are the important one...not others. Worry about yourself and ENJOY life and don't let people walk on you. Remember to walk tall and carry a big bat, and a cool theme song walking down the street will help. :)
To gain self confidence, you are first required to appreciate yourself and ignore any negative comments from people. Learn how to maintain eye contact and practice on how to make speeches in various occasions. Get some more tips from http://www.ehow.com/how_2148008_gain-selfconfidence.html.