If you are in a relationship, you may have fallen into the habit of taking your girlfriend for granted and generally not being the best boyfriend you could be. If this is the case, you should take a few steps toward being a better boyfriend. These are not "magic bullet" solutions, but rather, a set of day-to-day, consistent actions you should take regularly in order to make yourself a better boyfriend and make your relationship better for both of you.
Listen to her when she talks to you. This does not mean pretending to listen. Rather, it means actively listening, rephrasing what she says and making decisions based on what she told you for future action. For instance, if she mentions that she likes something, you can show that you were listening by getting it for her as a gift a couple of weeks later.
Spend time with her that you would not have otherwise spent with her. This does not mean that you should spend all of your time with her, but just that you should sometimes make it clear that she is a priority. If you usually spend your Wednesday nights at a bar with your friends, change your plans this Wednesday and watch some DVDs with her. By doing this on occasion, you are showing her how important she is in your life.
Compliment her often, but not predictably. Your compliments should be unexpected and from the heart; if you can think of something nice that you have just noticed about her, tell her.
Tell her what's on your mind. Good relationships are based on communication. So, if you're worried about the direction your career is going or if you are having a bad day, or, conversely, if you feel great about yourself because of something that happened to you, you should tell her. This will make her feel more connected to you and, therefore, make you a better boyfriend.