You gotta make sure you understand the concepts. The first time I took Calculus I failed, but I did learn how to compute derivatives, anti-derivatives, and do optimization problems. The second time I took it, I committed to remember every thing, that is every theorem, Rolles Theorem, Mean Value Theorem, Squeeze theorem, properties of limits, derivatives, and integrals. I studied probably 2-3 hours a day, depending on how difficult the material was.
When doing the homework, I recommend to keep working on it until your answers are correct, if you are able to check the back of the book. The least you can do is to work until you get them right, if not work to never get them wrong.
Another tip is before exams, practice on review problems, and on the night before get as much sleep as you can.