The basics would probably be beneficial. Things like what is profit and how to calculate it. The difference between profit and revenue. The difference between strategic and tactical decisions/objectives. What you'll need to know will differ from one exam board to another (I'm on OCR). Plus, they won't assume you know anything before starting the course so I wouldn't worry
Well, I didn't really know much, ie I didn't take it as a GCSE subject but over the summer just read up some topics it definetly does help as you at least have some sort of idea of what's going on and the first year of AS is always a summary of the two years at GCSE levels, don't panic!