This is my advice for if you are doing Edexcel:
Do the first 12 questions of a few past papers, go back through and mark them, identify where you lost marks, and go and revise those topics using online resources and YouTube videos. The first 12 questions on each paper are always by far the easiest, and it would be a shame to lose any marks on them. Make sure you get to the point where you are consistently getting 90+% of marks on the first 12 questions, these are free marks.
After that, make sure to learn all the formulas. I know there’s a lot to learn but these are so so so important.
Tip for the exam, right down EVERY SINGLE equation you do and formula you use, even if you don’t get the answer right you will still get some calculation marks. I don’t care if it’s as basic as 4 x 4 or if it’s literally just writing down that the area of a circle is pi r squared, this will get you boost your marks.
Make sure you revise the topics that usually come up for 4, 5 or even 6 marks. These big marker questions will benefit you massively if you can get some of them write. First off I’d recommend mastering the topics you already know you can get some marks on, then move on the topics you find more complicated. I’d recommend learning circle theorem as well as everything related to angles and shapes (I don’t remember the topic names) as this was what most of the big markers were.
Finally, make sure you prioritise revising for the paper you have first. If your first paper is a non-calculator, don’t waste your time revising for calculator questions, do that when you have an upcoming calculator paper, and vice versa.
You should get atleast a 6 anyway, in my experience people tend to perform better in the real thing than they do in past papers or mocks, but even still you should definitely revise in order to guarantee yourself a 6 and maybe even push for a 7, which is an A and will show universities in the future that you are competent in maths if you don’t do anything mathsy at sixth form