Depends on what you're good at. For me it was languages, particularly French. Didn't put much effort at all into French and German but came out with A*s in both. But then for example, with Maths, I got an A but I had to work really hard at it, and that was a retake!
Edit: Also, with languages, I believe that you're either good at them or you're not. Sure, you can work to improve, but it's not like chemistry where you can be crap at it, not really understand, but just learn the revision guide and regurgitate it in the exam.