First of all, you should be interested in your major. If you are not interested, self-study will be difficult.
Second, after choosing a major, there should be books dedicated to the exam, which are used for the exam. To learn these courses well, you can't just read these books, especially theoretical ones. Read relevant basic books. You can refer to the same course offered by the same major in the university and see different versions of the teaching materials.
Third, if you have the conditions, taking a little class at the university will be of great help to your study.
Fourth, you should have perseverance. Self-taught examination is a protracted war. Only those who persist to the end can succeed. Therefore, you should have a detailed study plan and finish it every day. Don't rush to the exam time.
Fifth, we should arrange the order of learning courses reasonably, generally combining with your examination arrangement, from easy to difficult.
Finally, I wish you early success!