Do things you can be proud of. You can't just snap your fingers and change your outlook. You can do things to prove to yourself that you are a worthwhile person by helping others. Then you can go from having low self esteem to being humble, which is way more awesome and doesn't require expensive head shrinks.
The best advice I can give you is don't give a shit about what people think about what people say or think be more outgoing and more excited about the joys of life, I'm not what most people call "preppy" or "emo" or whatever I don't care about it I dress the way I want like I wear flannels and skinny jeans and I feel great as a person!