I only started revising in mocks but I felt well prepared for most of my exams. I wouldn't suggest you to do too much because gcse's don't have that much content and it gets boring revising the same thing over and over. I'd have a look over the course, do like revision cards all year for each topic you cover. And as your going along, do like questions in the text books or buy revision guides (this may be better as answers are here) and do little end of topic questions as you go along. I'd do questions before like topic assessments. Or if you don't have one, as soon as you end the topic, do some questions.
Also, READ THE SPECIFICATION. I only realised the beauty of the specification after my mock exams. It will help you word answers well.
The most important thing is just to understand everything you've done.
If I had done this, I would've like fallen in love myself. But since I'm an idiot, I had to cram and revise like 11 hours a day before some of my exams. Not highly recommended. Also, because I hadn't had a good look at the spec, I realised that especially in the sciences there were quite a few topics we hadn't even been taught. So I had to teach them to myself the day before the exam. Try and avoid this :P
As someone else said, for history timelines are the best. For maths, I wouldn't recommend doing revision products. It's just practise. You might want to draw out circle theorems but that's about it. You get given the formulas anyway (except additional maths). Good luck!