1) Make Notes
Hopefully you will have notes from class, but if not make sure you go to someone in your class or look up the subject online so you can take notes and get an understanding of what you have to learn. It's really helpful to have these notes in your own words as this can be so much easier to remember.
A great idea is to set aside certain hours of the day for your revision, this will make sure that you will have as much time as you need and will keep you organised. Remember to stick to it though, otherwise there would be no point. Also, people can generally only concentrate for about 40 minutes at a time so give yourself breaks every so often so your brain can rest.
3) Start Early
There is nothing worse than sitting down the night before a big exam and trying to cram all the information you need in a few hours, this just won't work. Start to revise at least a couple of weeks before the exam so that you don't get that horrible last minute panic. Going in to an exam feeling prepared and calm is ideal.
4) Find Somewhere Quiet
This one really is self explanatory, but make sure your workspace is clear from distractions, this could be loud noises or clutter. Also turn your phone off because if it goes off every 5 minutes you'll never get anything done!
Sometimes if you don't quite understand a topic it can be useful to find videos online explaining all you need to know, I am revising for GCSE science at the moment and if any others are I would highly recommend checking out My GCSE Science on YouTube ( http://www.youtube.com/user/myGCSEscience ) I find this so useful for watching and taking notes down at the same time it really helps me revise.
I hope this has been helpful and if anyone has any ways of revising that work great for them I'd love to know! Good luck!