I personally found that rereading the textbook over and over again kept the facts in my head. If you can, buy your course's revision guide and/or the textbook and keep reading it over and over as if you were reading a book.
It's very possible that this method may not work for you but if you can it is at least worth a try. Other than that, knowing how the examiners will give you marks is another big thing. When I was doing GCSE History a 12 mark essay would need exactly two 'for' arguments, two 'against' arguments and a conclusion. This was for CIE, not Edexcel, but the the principle of knowing how you are going to be examined will make a massive difference.