How to be a good boyfriend, keep the girl you want and have her bragging to her girlfriends about you. Make them all jealous.
Listen to what she has to say all the time (even if you don't agree). Hear her out, and then make a point either for or against what she has said. When you don't agree, be polite. Name calling and put downs only make you look like a jerk.
Don't go on and on about topics you know bore her. Some talk is OK, but keep it under 30 min. at any one time.
If she's not in the mood for intimacy, don't press the issue. This statement can be applied to any number of situations, and it is ALWAYS good to respect her.
Be honest, respectful, and loyal.
Be well groomed and use good manners. This is especially important when you are with her family.
Never forget an important date. You can set up email reminders to help you out. The gesture doesn't have to be grand (e.g. - an e-card or verbal mention) as long as you remember.
When you go out don't complain about prices. If you can't afford to go out, plan a date in.
Don't brag to your friends about your "prowess". Conversely, don't talk about problems between you to others before you talk to her. Both will hurt her.
Accept her for who she is.
If you choose to end things, do it in person. By phone is only ok if you are long distance email and text message/facebook/instant messenger are never ok.