I got 12 A*s.
My advice is to try and figure out different revision techniques for each subject as each one will have different methods that will work best. E.g with English Lit I just planned loads of essays whereas with maths I made sure I knew how to do each thing.
I did further maths which was really hard being in year 11. The only reason I got an A* was because I went through the whole textbook the weekend before. I know that seems like cramming but it really wasn't; most people didn't even revise for it as it was stupidly hard!!
GOOD LUCK TO ALL, GCSEs are not impossible and you'll be surprised on results day if you have worked hard