I found the best way to revise for maths was doing practice questions. The site I used was Maths Genie. They have loads of questions organised by topic which can be really helpful if you just want to revise a certain type of question. There are also past papers you can access - I think it's a good idea to time yourself doing them so you can get used to what the exam will be like. If that's not enough I suggest asking your teachers for more questions just so you can get used to the question types and using the formulae and methods in an exam type question.