For maths, papers upon papers upon papers (that's the way I do it anyway). Past papers are always good, or practice papers if your school has made them. Usually I start with one paper and allow myself to use my notes if I need to, take note of what I had to check, then read over those topics and make sure I understand them. Try another paper without notes, mark it, see what topics I need to read over this time. Keep going until you don't need to read over notes anymore.
Also, YouTube videos can be good because sometimes having something explained in a slightly different way can make it click.