If I need to learn and memorize some material well, I use the "questionnaire-responder" method:
While reading some material, I think about what questions can be asked based on what I have read (what questions I might be asked or what questions I might ask based on this paragraph \ page \ text).
I write down numbered questions in one notebook.
In the second notebook I write down answers to the corresponding questions with similar numbers.
As I write down questions and answers, I reread them, and then I also repeat them in separate blocks (as questions and answers accumulate).
In addition, thanks to this questionnaire-responder, you can quickly repeat the material that you learned before, but after some time forgot.
Try reading from the end. The most necessary information is there. And with the study of the end, you begin to clarify the moments closer to the beginning. Since conclusions are usually drawn at the end, it is very easy to skip the water in this way.
It's simple - choose the most important information given to you and focus on it, namely: exclude water and unimportant moments. In general, it all depends on the specific case. Ideally, it would be to write down the most interesting things for later memorization. If this is inappropriate, then just remove all unnecessary in your head and leave useful and important.