I failed my AS exams first time round so so badly. I got UUE because I just didn't care at all. I dropped Biology and Health & Social Care to pick up Religious Studies and Business Studies, as well as starting Psychology all over again.
I ended up doing a lot better. In one Psychology exam I did the first time round I got a U, and that same exam after retaking turned out to be an A.
I did do Biology the first year and all I can suggest is doing past papers after past papers. The questions for AQA exams are generally the same a couple years apart, just worded differently. Do posters and notes constantly then the past papers. Worked a charm for my other exams!