1. Never take anyone's opinion seriously unless they mean something to you like your family's.
2. Do not compare yourself with other people. I honestly have yet to accomplish this rule, as it seems almost natural to look at someone and compare yourself. But no matter how hard you try you will never be that person, you have your own skin so you should embrace it.
3. Don't like something?Change it. Even go under the knife if you think that will make you happy, don't dwell on features that you dislike. For example, think you need to loose a bit of weight? Then loose it.
4. Get rid of people who put you down. TRUST ME it feels like a huge weight taken off of your shoulders. If people are mean ignore them because once again their opinions do not matter as you're probably not gonna know them in a few years.
5. (finally) Treat yourself. It will instantly make you feel better and therefore more confident. Whether it be buying something as a present to yourself, or something simple like a soak in a bubble bath. Whatever floats your goat^_^