make notes constantly through the course, this will help when understanding idea's (even if you don't get it when your writing it, it'll help you later) Make notes from what your teacher says, but also go through your course textbook and make notes. After each lesson go over what you've just done (although i never do this due to being dead lazy)
when it gets to one/two months before the exam re-write all your notes, making sure you thoroughly understand everything you're writing down. Only once you think you understand everything well enough, try a past paper. Get this marked or do it yourself with a mark scheme. Look at where you went wrong and revise it. Then as pretty much everyone has said, go over as many past papers as you can, ideally all of them. On the last few you try you might wanna time yourself.
similar to maths, you really have to put in the hours if you want the best grade your capable of.