Best advice anyone ever gave me was "Don't make mistakes". By following this advice alone, I topped ext. maths in prelim at a selective school. On a more serious note, in terms of every night, do however much is needed for you to FULLY understand the concept. For example, when we were doing polynomials in class, which I found really simple, I might just do the last extension questions in Cambridge and be done in about 10 minutes. For other areas that I found more difficult, e.g. circle geo (my enemy), I would do the textbook questions and then heaps of past paper questions as well just to make sure I could get it.
Also, I would disagree big time with what jetblack said. Start doing past papers from now. You can easily download over 400 trials from the net, find questions from topics you have done and start now, there's no substitute for actual exam questions.