Look at the Compass site for sample problems. Practice with these to give yourself an idea of what to expect on the actual exam.
Review your high school algebra, geometry and trigonometry text books, as they cover similar material to the Compass test.
Visit your campus math tutoring lab if you are having trouble with a particular type of problem or area of math. The tutors there have passed the classes you're trying to get into, so they will know what you should focus on.