Use a range of past papers from previous years to help you organise your revision. You should focus on revising topics that you are weakest in so identifying topics addressed in each paper is a good place to start. Once these are identified you can then use specific past papers to help you revise this content. 

Using mark schemes is an excellent way to improve your knowledge. As well as helping you to understand how marks are awarded and what was required from each of the questions you answered, it will also help you to see where you are losing marks and what you can do to correct this. After marking your work. Work on identifying any mistakes or knowledge gaps. Note these areas and dedicate additional time to revising them.

It's always a good idea to read the examiners' reports for past exams. These are written by the people who mark the exams. and they write a report on each exam paper explaining what they wanted to see from students and where students went wrong. This is an amazing resource for understanding exactly what's expected of you in an exam.