Hi, I got grade 9s for all 6 of maths, sciences and English GCSEs, so I thought I might try answering.
I found science and maths GCSEs easy, so I didn't put in much effort; I focused on only the harder grade 8-9 questions. I also used pmt (physics and maths tutor) to look up for more questions.
For English lit, however, I spent about 3 hours every week writing at least one paragraph of every possible question on themes they could ask (because my idea was that you can always link multiple themes to one character, so you will definitely have practised any question they can throw at you). I also made flashcards of my favourite quotes (about 3 per text). Poems are the more tedious ones; I looked at all the poems that had come up, guessed what would come next.
For English lang I just read a lot of historical fiction after school (made myself spend an hour every day at the local library) and prepared a piece of fiction before Paper 1 because the question they will give is very broad. Paper 2 was just a shot in the dark (somehow still did well tho?🤔)
I would also recommend learning all the AO marks by heart so that you can see your own work in the eyes of the examiner and know what they are looking for (yes, this kind of works like a checklist).
I probably did more work than most others for English because English is not my native language. So be aware that you might not have to go as extreme as I did. I would also recommend Mr Everything English and Mr Salles on youtube because I think their strategies are more efficient that whatever my school taught me (which wasn't much!).
I'm quite out of touch with GCSEs since I'm in y13 now so I can't help with the specifics but someone else here probably know better than I do. Sorry for the lengthy answer!