Do not select your classes without speaking with your academic adviser and reading the course catalog. Make sure you have successfully completed any prerequisite classes. Ask your adviser about specific professors and take classes at hours of the day that you are comfortable with.
Organize your course material and buy your textbooks before classes start. Keep track of deadlines, test dates and other important details in an agenda book. Plan a weekly homework schedule for each class and stick to it.
Take advantage of on-campus tutoring and professors' office hours. FInd out ways you can do better and attend any test-prep classes and review sessions.
Drop classes that you will most likely perform poorly in. Find out the deadlines to drop a course and talk with your adviser about possibly dropping a course and adding another that is more suitable to your academic goals.