I have said this before tons of times and I will say it again. Start early. Really early. If I were you, I would have started revising in the summer already for stuff you have done in year 9 and 10 so you are confident with the basics and ready to move on to the hard stuff. I would also suggest you to start doing past papers even if they are of the old spec because exam questions are similar and the concepts behind them are similar. Make notes, flash cards or whatever suits you and revise everyday. Since your mocks are coming up, I think it is high time for you to practice your time management skills as well because I feel that most students struggle with timing the exam hall as they are under pressure (some for the first time in their lives) and the nerves can really let you down sometimes (talking from personal experience as I experience in my english exam). Otherwise, make sure you get enough sleep and drink plenty of water.