I did 4 A-Levels and wouldn't recommend it unless your offer specified such grades. I did Maths Chemistry Physics and Politics. I was fairly good at Politics and it was comparatively straight forward so that got sidelined for much of Year 13.
Maths and Physics were fairly similar (which helped) and revision methods for both tended towards completing past papers and targeting revision on questions where I went wrong (unless it was just stupid mistakes that I was usually competent with).
Chemistry was probably hardest to revise for due to the massive variation of topics and questions. I stuck to revision guides/text books, read through a page and answered summary questions. When I was fairly confident I'd move onto past papers.
Started revising properly for Politics about a month before the exam, which was probably a bit late, but any earlier than that would have taken time off the other subjects.
In the end I ended up with AAAB (B in Maths) from AAAA at AS. In hindsight I wish I'd dropped Maths at the end of Year 12 cause I'm pretty sure I could have got A*s in Physics and Politics with that extra revision time as I wasn't far off any way.
Having said all that, I was a lazy Year 13 so I'm sure if you're really committed you can handle it. Just don't over-face yourself with work cause that's when you start to panic and that's no good for anything. There's plenty of time yet to boost up your grades, best of luck!x