Make sure you understand processes and how to determine what to use for different questions. You might know something but the context that it is placed in may be confusing.
Also if there is anything that you consistently cannot get right on a paper then make sure you practice those types of questions. I used to hate surds but I did some difficult surds papers. I now hate surds even more but I can answer them consistently. Think of that same consistency as a guaranteed mark that you will achieve and then over time you can amass more and more of these marks.
The best revision for maths personally is past papers, but that's already been said a lot. In these papers, though, note down any questions that you struggle with or maybe don't feel confident with.
tl;dr - Past papers are fire