After class, you can react with the teacher and let the teacher pause a little in more important places.
Moreover, mathematics is a comparative study of thinking. Don't bury yourself in taking notes in class, you'll lose the train of thought the teacher said. Pay attention to follow the teacher's ideas, write down the important places little by little, and be sure to read them after class. Let yourself fully understand the whole thinking direction, quickly forget your thoughts or ask questions, and you can't accumulate them. Once accumulated, it will be very troublesome to make up.