I got AAAA at AS though with UMS scores of 99%,97%,86% and 83% and I only really revised a couple of weeks before the exams, cramming is the most effective revision method because how you supposed to remember what you revise now for exams in May/June?So cram all your revision a couple of weeks before and you should be able to remember most of it.A lot the modules don't really need revision its just best to to be on the safe side and to get the highest possible UMS.