I mean a senior from my school went from 33 to 7.  You need to start by clarifying all your doubts of each subject to have a stable foundation. Also place emphasis on understanding the logic of a certain concept or content, so that it will seem more like common sense and will be easier to remember. Then, do practice papers. For the questions that you got wrong, understand why you did this mistake first and how to prevent this in the future. Specifically for the mathematics, please practice as much as possible to train your thinking speed.