You need to review material you are not familiar with. The only courses I was able to pull a 4.0 average on were courses that I knew the syllabus for before I even walked into the first lecture (like how Bart Simpson knew everything in kindergarden, or how you should know everything that is taught in grade 5 or 6.

In any case, as I said, you need to review your material. Pay attention in class, ask clarification questions, and attempt to do the homework. If you need help, ask for it.