Last year, when I read a book for the third time because I couldn't remember its contents, I decided to do something about it. After experimenting many methods I found this single hack most working, still simple. It helped me to remember most parts of the books I read and only rarely look into them (to find specific details). Want to know the hack? Here: Make Notes As You Read. Have a digital book? No problem. There are loads of applications to highlight and make notes.