Maths = I just did every single past paper tbh and always went to my teacher if I didn’t understand something. I didn’t really use that many online resources apart from thegcsemathstutor on YouTube - he is fantastic!
English Language = know exactly how to do each question ie how to structure it. I only revised the week before and managed to get a high 9 just because I read books and studied examiners reports. You can take inspiration for creative writing from books like Jane Eyre that has lots of landscape descriptions. For persuasive writing READ THE NEWS and watch political debates just to make your writing sound eloquent.
English Lit = know your quotes. Read critical essays if u can eg. on jstor. I personally didn’t use Mr Bruff or Mr Salles because if you want to distinguish yourself, you have to use better quality and unique analysis.
Science = PRACTISE PAPERS. I literally did every one since 2010 - imo it’s the best way to learn.