Try to take an interest in the subject you are studying. Try to find out what the subject is all about and determine the real purpose for you being in the course. Make notes of what you study as well as taking lecture notes. The previous suggestions will not help you if you dont make yourself follow them. Willpower comes from practice.
Willpower is developed by making positive behavioral changes.
Learn to read more efficiently. Constantly try to increase your reading speed and your comprehension. Pay attention in class and concentrate on what is being said. Often we think we have forgotten something when in fact, we didnt use our learning processes to begin with. Increase your vocabulary.