Go through the theory. The text books are ok for practice questions, but it's often difficult understand the theory in them because a lot of them are typed in a way that makes fractions and other mathematical syntax hard to read. If you can, try and find a set of workbooks that go through the theory of the course with someone having written it out, instead of typed. My teacher taught us the entire course like that and it helped a lot.
Once you under stand a concept, do a couple of questions so that it sticks, then move on. Come back to it a bit later, maybe at the end of the week or something to revise it again. A lot of the concepts and questions aren't all that hard, but if you don't do them for a long time you will forget how to.
Other than that, just study hard, and make sure you know your three unit course pretty well. The entire three unit course is contained within the four unit course and up to 30% of it can be asked in the final exam. Not only that, a large part of the theory is developed using methods from the two and three unit courses.