The most important thing is to restore the examples in books.

If you come up with a difficult problem, you should combine several examples. As long as you see the doorway and answer them one by one, there will be no problem.

For the wrong question set, it is best to put the same kind of questions together, see what you did wrong before, and where you made the last mistake, sum up the mistakes and find the correct answer. Every time you make a mistake in the problem set, do it yourself first, and then see if you will make the same mistake again.

It is most effective to misread the problem set before the exam, because it clearly shows your mistakes and correct answers.