Organise yourself. How many exams do you have? When is your first exam? Do you have any clashes? Then prioritise which subjects you need to focus on and within those subjects which units/topics you need to study in more depth.
Revision Timetable. Create a revision timetable (see links, where you can create one online or use a template) make this as detailed and specific as possible. Also plan in breaks for praying, eating and relaxing.
Get Revising and Testing. Continuously assess how useful the revision is by attempting past papers. These are available online through the exam board websites.
Learning style. Decide what type of learner you are. Some work well with visuals (post it notes, highlighters, diagrams) others learn through memorisation techniques (mnemonics summarising texts. Decide how you will revise each topic and ensure you have the right resources to aid you to do this.