How Do You Motivate Yourself to Study?

I'm in college now and my grades are dropping. I have a 3.1 GPA now. Basically I can get a lot of things really fast but I have a problem paying attention in class. I always start off strong then I just stop caring. Even without studying I can do better than most people who study. BUT… towards the half way mark I can't pay attention in class. So in order for me to do good I must study, but I don't . I don't even need to study that much to get a subject down.

Suggestion:

Well, I would think about how it affects your grades. If you know there is a consequence then perhaps you'll try more to pay attention and study?