after each past paper, note what topics and style (mc or short answer) of questions you got wrong (esp for fundamental errors but also silly mistakes), then focus on those topics by rereading the textbook / chapter review / past hsc qs
Ima be honest maths is the kind of subject where you cant waffle or yap, you gotta know the why and how. Its not a subject u can cram like humanities or english. I finished the advanced course 5 months before trials done 100+ math adv papers this year and I still only get 90 raw. My mate started doing past papers a month before trials and only got 45. He ended up doing 12 before trials.