Take an acceptable number of credit hours each semester, but don't overdo it. Overloading your schedule can make it impossible for you to efficiently study for each course. Full-time enrollment is 12 hours per week, but many students need to take between 15 and 17 hours to stay on track to graduate in four years. On average, you should study three hours per week for each credit hour you take. So, if you have two courses worth five credit hours each and two courses worth three credit hours each, you are taking 16 credit hours and should study for 48 hours per week. You may need to study a little less or a little more depending on the difficulty of each class. Two credit hours are the equivalent of two semester units of credit or three quarter units of credit. Divide quarter hours by 1.5 to get the equivalent number of credit hours.
Learn effective note taking. A class lecture can give you hints on what the instructor feels is important and possibly what topics may be covered on the next exam. This can be a much better strategy than trying to remember what was said in class and taking your notes from the reading materials only. Focus on capturing the "meat" of what is said, in as few words as possible. Pay attention to repetition during the lecture; if the instructor says it more than once then it is likely important. Review your notes regularly as well as directly before an exam.
Retake classes to get a better grade. If you have already taken a course and received a poor grade, take the course again. It may be easier the second time around, since you already have some background in the course. Since retaking classes can prolong your road to graduation, you should focus on courses in which you received a "C" or lower. Also, a class you are retaking may not be counted toward your total credit hours for full-time enrollment, so you will need to take a minimum of 12 credit hours on top of the class you are retaking.