The night before - some light study. This could be going over the priority points (some of which you still may not be sure about), doing some further practice questions or simply going over key topics.
Obviously I don't recommend staying up too late, but i'd try and fit in at least 7 hours of sleep at the minimum.
On the day, don't do much. I'm personally against any study on the day of an exam. Have a good sleep, a good breakfast and make sure you're energised for the exam. You need to be confident in yourself that you've retained the knowledge that you've learnt throughout the year and apply it when you enter. You will most likely work yourself up if you start studying your notes on the day. This will lead to doubts and worry, and these don't help anyone hours before an exam.
Best of luck all Year 12's (and other students doing 3/4 exams!)
