Don't waste your precious time doing mind-maps or reading textbooks. That kind of thing is helpful for History, Georgraphy and English Lit, but it won't help much for Maths. It does my head in when pupils tell me they've beein doing that kind of thing. If you don't know what specific topics you need to revise you just need to jump in and get practicing - you'll soon find what it is you need to work on.
You get a question, you answer it. You check to see if you are right. Simple. Don't do lots of maths without knowing whether you are getting it right or wrong - there's no need to do that now in the age of the internet.
If you're revising for mock GCSE exams or the real thing you probably want to do some past papers. The best and easiest way to do this is to visit the Maths Genie because all the past papers available are up here with solutions so you can check that you are right. If you want to see how you are doing as you move through the paper, try one of our full GCSE practice papers on Mathsgrader, foundation here, and higher here
I hear you. There is a tool on Mathsgrader which is designed for pupils to use which will allow you to quickly reach questions which are appropriate for your level and grade. The Foundation Grader and the Higher Grader will move you up a grade each time you get a question right. This means, if you are trying to reach a grade 4, you would be reaching that level of question very quickly and you, as a pupil, can be sure that your revision is making a difference. If you do 15 minutes a day of this over a month, you should notice the difference.