How to be a really good girlfriend?

First of all don't feel self conscious. While I realize nobody's perfect, realize that you have many more strengths than weaknesses. Right off the bat, the fact that you're seeking to be a 'better girlfriend' is already attractive. Unfortunately when it comes to your current boyfriend, you can't actually go in his soul and start flicking switches to keep him around, that whole deal is up to him.

But-

You can make yourself a more attractive package. The important thing to realize is that you should improve yourself, for yourself. Pick up something like painting or writing or anything that will exercise any given aspect of you and stick with it. Don't try to compete with his ex girlfriend. You're too good for that.

Now from a guy's point of view, other than the physical stuff, comes her talents. What makes her special? What does she normally do with her time when she's not with friends or at school? Is she unique? Sense of humor? In the end, a guy will normally stick around if she's really interesting, (and of course fun to fool around with ;)).

Also, pay attention to his needs. Talk to him, get him to communicate his thoughts and intentions of things. Try to make yourself a bigger part of his life and try to take interest in the things he may find interesting. Just don't let it get to a point where it stresses you out.

Just be open, fair and honest. In the long run, life usually works out to your advantage. Enjoy.