The first important point is to recognize the differences between high school and college. Usually, one of these differences is the degree of self-sufficiency and self-motivation expected of you. Your professors except you to attend class, complete assigned readings (including the problems at the end of the chpater), hand in assignments on time, show up to class on time and participate. You can only participate if you have pencils, paper, a calculator and previous notes you have taken. Professors are only human, and they tend to match their level of concern with your level of involvement and effort in their course.
Here are some suggestions for specific areas: