Alright, I'm a little late for this, but the best piece of advice I've ever heard is:
Be yourself. That's it.
Don't pretend to be someone you're not, don't try to change yourself just to meet someone, that's being rude to the girl.
The best thing to do is just wear what you want to wear. If you throw anything on that you feel comfortable in, keep doing that. If you like a certain type of style, do that. It doesn't matter. Even on dates, don't try to look really fancy. It makes it look like you're trying to impress her by being someone other than the person she likes.
If a girl doesn't like you for the way you are and the way you act, then she isn't worth your time. Relationships are about appreciating each other, not changing each other to fit exactly what you want. Yes, there are girls who will like you for who you are.
Another thing to remember... If you're not happy with yourself, that means you should fix whatever is making you unhappy. Overweight? Take steps to lose it. There are some things you can never change, but there are a lot of things that you can change until you're happy with yourself. I'm happy with myself, even though I'm a little overweight with hair that goes down to my waist and old, worn clothes. I'm comfortable like this and I don't care what anyone else thinks of me.