You know what makes the difference?
Take a walk, or catch a train and think about what you read. Find the main ideas and how the material relates to yourself. Play with it and ask yourself questions about it.
Then next day try to answer them in paper without extra material. And only after that reread the book to check or find unsolved the answers.
Learning is hard. There is nothing as easy learning. The good news is that it can be hand AND fun.
About reading:
Engage in every sentence, ask yourself what the writer is trying to tell you in every sentence, after that translate it to imagination and relate it with yourself and what you already know.
There is shallow reading and deep reading. Deep reading is a must for technical books, but also a joy for fiction. I still remember so vividly the coldness and texture of the walls of the hobbit's first mountain tunnels despite haven't been told about it.