I took very detailed notes in lessons and revised all of the course in great detail for exams. By taking the detailed notes you learn more in lessons and have great revision resources . In addition, practice exam technique, with exam questions , open book if you want . You don’t actually need to know loads but understanding the links between all sorts of topics helps you be evaluative and you have no shortage of facts to use in exams. I loved history so worked really hard for two years and got a 9-I think my earnest interest in the subject helped far more than getting a top grade for arbitrary reasons because I put in so much effort without thinking. Essay technique is still super important no matter how many facts you know so work on that .