Brutally honest: I worked a lot. And true, it annoys me when people lie about how much work they've done - 'oh I did 3 essays before the Eng exam and I got a 50' - some friend's friend said that.
I think that you can ensure a high mark in any subject with pure hard work. I went to the Methods exam feeling confident I would do well. I did tonnes of trial papers, did most of checkpoints by June, did ExamBusters, Neap, A+ notes, A+ exams etc - you will find that most people who DO get high in Methods have done a lot of work. Maths subjects = practice, practice, practice. Do tonnes of practice exams - this REALLY REALLY helps. Especially if you're motivated enough to give yourself reading time, checking time etc - you'll find the improvement amazing if you persevere.