Hiiii, I haven't gotten a GCSE grade yet but I am predicted a 9 and in mocks I got 88%. What I did were past paper questions. Start with the ones by topic - you can find loads on physics&math tutor. Screenshot the ones you get wrong the first time and re-do them. Then move on to past papers. Do the 2018-2021 ones including the reserve papers. If you're aiming for an 8 then make sure you get 70%+ on all of them, and if you don't, re-attempt the paper. Keep the 2022 and 2023 ones for study leave or closer to the exam. Memorise the mark schemes for salt preparation, etc, like the long answer questions that keep coming up with little variation.