Before the Class: Browse the text book to see what would be covered in the next class. Mark the places where you think you may have difficulties to understand.
During the Class: Actively involved in the class by paying attention, asking or writing down whatever questions you may have related to the lecture.
After class: Review the text book, lecture notes, examples presented in the class and the text book. Try to answer all the questions you have in the class. Do the assignments. If you are stuck with some problems, go back to the text book or your notes to see if you can find a similar problem. If you are still unable to solve the problem, it is time to see your instructor or TA.
Don't miss the class. Pay attention to each individual quiz. Do not just rely on the next one to improve your grade. Do all the homework assignments on time. Go to the office hours regularly. Check your understanding regularly, for example, weekly. Make sure you don't get lost in the middle of semester. If you get lost and do not catch up, it would be a disaster for the rest of semester.