Read more and recite more.
I haven't read the book that teaches you how to teach yourself, but it doesn't matter if I do, because the method of self-study is very simple. I have read too many articles and recited too much, so I can't read any more. If you are always absent-minded, copy a book. I don't know whether you like calligraphy or not, and you copy the book neatly, but usually my heart has gone in before copying the next chapter, so I can study normally.
Do more exercise.
If it's a rational subject, it's best to find more problem sets, which are also available online, but I like to buy them from ordinary universities in bookstores. Of course, before the book passed the exam, I was doing off-topic exercises for a while. I couldn't answer some basic fill-in-the-blank questions in the exam, but I did well in the big questions behind, and I thought it was too easy.
Make a mock test paper.
The exam is coming. (Of course, this is in your work schedule, not suddenly "taking an exam". ) I usually leave a week or so for the next day to do the simulation test paper I bought. I think it's useful to do this without self-confidence. There are generally ten test papers. List the daily results and make up for the mistakes. At least understand the wrong questions every day.