Thorough revision is the key to success in exams, and to be really thorough, revision has to start with plenty of time to spare. Attempting to cram in facts at the last minute is a poor substitute. Unfortunately, when exams are still in the distant future, you're not likely to feel like spending time revising when you could be relaxing and enjoying yourself. The key to early revision is a clear schedule to help you keep motivated.
Make a list of the topics you need to revise before your exam deadline. Rank them in order of importance, or how much effort you need to devote, to do well on the exam.
Mark down your exam deadline on a calendar, and mark down your existing time commitments. Then, schedule revision blocks within the remaining time. Do not attempt to revise all the time. Each revision session must have a clear beginning and end time. Be realistic about the time you can afford to commit. Schedule revision before leisure activities, so you can use them as rewards to yourself.
Find a revision partner. This doesn't need to be someone who will actually revise with you, but someone who will help you stick to your revision timetable. In return, you can help keep your partner motivated.
Schedule breaks. If you revise constantly, you're going to burn out long before your exam. Periodically give yourself a few days without revision, in which you can take time to relax and do things you enjoy.