My top tip would be:
Before you start revising, do something you enjoy. Listen to your favourite song, read a chapter of your favourite book, play a piece on the piano etc. And when you've done that thing that you enjoy try and learn something, just take five or ten minutes to read it through and make sure tha you understand it (that bit is key, don't try to remember something that doesn't make sense to you, I've made that mistake before and I can tell you it won't work out). When you understand what you are trying to remember, go back to the thing you enjoy doing for a few minutes then learn something new, do the thing you enjoy and then go back to the first thing you learnt to see if you know it.
Repeating what you're trying to learn is the best way to remember something, but by breaking it up with something that you enjoy doing it will motivate you to try your best and not give up.
Best of luck with your exams, let me know if this helps and how your exams go