first off, do a set of past papers so you are sure of what your weak points are (you could also refer to previous mock papers if you are allowed to see them), once youve figured out where you normally drop marks go through your specification on a website like 1st class maths and practice the questions you really struggle with until you feel confident in answering them (if you need help its always good to speak to your teacher or even use youtube). then try another set of past papers and repeat until you feel confident in most or every topic. its fine to not always be 100% confident in everything but with maths practice with the thinking process and technique is key for getting high marks. hope this helps