Can you revise from doing purely past papers? Watch
Also something I'm not sure many people do, get the specification and highlight everything youre comfortable with and research and revise everything you don't know. Often youre not taught absolutely everything and there are new questions and awkward things that might not be in your textbook. I've done this for most of my exams (especially sciences and geog) and you always find things you havent learnt and the new awkward bits the exam board have entered.
But do use past papers a lot to then test your knowledge, this is a key to success that wasn't emphasised anywhere near enough at my woeful secondary school for my GSCEs and was constantly emphasised at my wonderful college for my A levels. I did significantly better during my A levels because of it. Essentially you want to get to the point with revision where you are a week or two away from the exam and purely be doing past papers. That way, you retain all of the knowledge you have built up (because it's constantly being tested), but you also learn how to structure answers properly (which is often key for A* grades and if you go to a terrible school like mine was, they won't even teach you).
Edit: As the above poster stated, 'specifications' are amazing tools for seeing what areas of knowledge you need to work on or not. Use them as a rough outline of the sections of your revision.