Its been almost 3 years now since I graduated from college. My early years were marred by less than adequete grades, but by the time I reached junior year I finally figured out the secret. It's based on 4 simple rules, some of which seem trivial but are absolutely essential. 

First: you have to start studying for exams a couple of days in advance, cramming never works.
Second: go see your professors and TA's for help outside of class, alot of times they'll give you a good idea of what to expect on up and coming exams.
Third: do your homework. It's worth the extra points and you learn exactly what you need for the exam.
Fourth: and maybe the most important, you need to get passed the fact that some classes require more work for the same grade.

Once you can accept these 4 principles, you will be successful. Notice, I didn't write "Go to class", as I had cut many lectures that didn't take attendance, and was still able to get a good grade. However, going to class is always a good idea. Just thought i'd write these down before I forget, and hopefully help anyone out there.