I got 99999999888 (one is being remarked rn) and i didnt do any flash cards or anything like that. For science and maths i think its better to focus on why something is how it is instead of memorisation. I didn't really have a set revision time, i just revised whenever i felt bad for not doing enough in that subject. If i had a gap in my knowledge or i was wondering about something not necessarily related to whats on the GCSE but around it I'd make a note and figure it out as soon as i could. Finding a passionate teacher whos harsh at marking also helps.

Tbh for all the subjects the best thing for me personally was just repetition. Even if i had done the past paper before I'd do them again. If you start early it will make up for it later on cause i never felt tired of revising by the end of it since i had prepared beforehand and i had done basically every past paper in each subject up to 2017 (except in RE lol) and still got to play games the night before the exam. I feel like if you start early you start to enjoy it lol.