Been there done that...
I can mark the day I understood the change that needed to take place in my life...I won't tell you how that came about cause its pretty personal....but in hindsight here are the things I found to help in that transformation.
1) Constantly work at improving yourself, everyone says love your self...I say love your potential, work at what you want and learn to admit when you are doing well and how to constructively criticize your self. For me this was weight loss and bass practice.
2) Don't be the person you are, be the person you want to be! I can't stress this enough....How can you "be yourself" when you define yourself...that pre-school mantra is such BS. Idolize someone, or a few people, it'll make life easier....you won't turn out to be them but it will give you an idea of what you want to do with yourself.
3) Party, get drunk have fun! Brooding gets you nowhere in life. Take risks! Like real risks, nothing makes you feel more alive than doing something stupid once in awhile.
4) Embrace change and when you like a direction you are heading then solidify it, start using new adjectives about your self (words like creative, attractive, intelligent, talented) Surely after meeting some of the people who use these words to describe themselves believe then I have every right.
5) Change your image, nothing makes you feel better about yourself than a new haircut or a new shirt.
6) Learn to see the insecurity in others, everyone thinks this way, you just think you are the only one...just observe people, everyone is covering up an insecurity, once you can see that you won't live in fear of their "perfection."
7) Listen to new music (not chronologically new, new to you) all the time, sometimes my tunes will put me in a funk and I don't even realize.
8) Self confidence is a daily struggle, don't let it bring you down, there will be good and bad days, but try to stay positive...if you are feeling negative do something good for yourself (like go to the gym) that day.