Efficient studying methods?

I’m due to start sixth form in September, studying classical civilisation, English lit and politics and I’m REALLY worried about my gcse results. I studied lots, but I’m worried that my methods were ineffective as it would take me like 2 hours to cover what others could in half an hour. I feel like I never learned to properly study as I could get good grades without trying, until my year 11 mocks, and by that point it was too late to teach myself properly. I’m especially worried about my science results, as I’m more naturally suited to essay based subjects , the way I would revise for them was SO stupid (I would literally cram half the topic onto a single flashcard, and try to memorise it, because it worked for English). Anyway, I’m stressing lots and I’m really worried that I’m going to repeat the same mistakes in college and fail because I spent 2 hours studying yet learning nothing. If anyone who does the same subjects I want to do (or just any essay based subjects in general) has ANY tips for how to revise effectively I would be SO grateful. Whiteboards, quizzes, note taking methods, I’m literally willing to try anything. Also, if anyone answers, please be as in depth as possible about how you took notes in class, then transferred it to to revision materials and how you actually learned it. Please.