One way to study is to do what you're doing now - read! Class time is a great opportunity to be introduced to new concepts and to see how they fit together with previously learned ones; however, there is usually not enough time to address details as well as a textbook can. In this way, your textbook is a second instructor that allows for more detail and more structured delivery of content.
Another way to study is to chat with classmates about the concepts covered in class. Believe it or not, just conversing about the topics in a thoughtful and critical fashion is studying. It keeps your mind on the task.
Most people think that doing homework is studying, but this is not exactly true. Sure, if you are concentrating on true understanding of the topics as you are going through a problem, then you are definitely studying; however, most students have too many distractions and they end up powering through the homework at the last minute. This type of "studying" is counterproductive.
Do you study at least two hours for every one hour of class time? If not, why?
How many hours do you dedicate to watching TV every week (on average)?
How many hours do you dedicate to leisure activities per week (e.g., hanging out with friends, going to the movies, etc.)?
Would it be too difficult to trade out a few of these hours for study time?