Go through your notes, make sure you understand the basics (by re-doing questions that you've already done to check you still know the method etc), have a look at some CGP revision guides for a rough outline of what you need to know. Then blitz the past papers - do all of the ones you can get your hands on. The same questions come up year after year (just with slightly different numbers, but the method is the same) and if you can crack the past papers, you're on track to getting an A*.