Wow..there are many ways to become a better boyfriend.
1. Listen to what is going on in her life. Nothing is better than knowing what is happening in her life and ask her how those things are going.
2. Dote on her AkA hold her hand, give her reassuring hugs, and try to make her feel like a princess.
3. Be Loyal...don't flirt with every girl you see...also keep your eyes focused on her. When she feels like the most important girl in your life, then you have accomplished something big.
4. Each Girl is an individual and wants to be treated like so. Spend some time figuring out her favorites.