First, according to your description, your biggest problem is that you have not formed a knowledge system, and the connection between knowledge points is your difficulty.

Secondly, I suggest that you read more books or do the problems that the teacher has talked about recently. This is not a simple repetition, but you have to use your brain to think about what the knowledge points of the topic investigation are and what is the connection between them.

Third, write down the connection between the knowledge points that teachers use at any time in class. After class, think about which one you didn't expect or didn't contact when you did the problem, so you can draw inferences.

Fourth, often discuss with classmates and explore your own ideas. Of course, the best way is to find a teacher to answer.

Fifth, remembering what the teacher said is the first and very important step in learning. You did it, but learning to use what you remember is the most important thing. It depends on your own diligence and persistence.

Sixth, we should learn from the wrong questions, sum up the shortcomings and find out the blind spots of thinking.

Seventh, do more problems, you don't have to really do them, you can watch them, but you should think clearly about the connection between the purpose of doing problems and knowledge.

I hope it helps you. I wish you success in your studies and be on the list.