Do not give up! The reason why I didn't learn well is my poor summary. Learning is summing up. Connect seemingly unrelated chapters, and you will find that each chapter is inextricably linked, and they are all related. I see, the grades will naturally go up. The other is to make the exercise perfect. The most effective method seems to be "crowd tactics". But do not be too difficult, be flexible. Still have to be good at summarizing the "motif", and any topic can't be separated from the "motif".

I wish you progress in your study!