Depends on your goal. 1. If you want to remember a book, so that you can write about it later in life -> start writing summaries after every chapter you read a

Depends on your goal. 1. If you want to remember a book, so that you can write about it later in life -> start writing summaries after every chapter you read and a final one at the end of the book. 2. If you want to remember details in the book, so that you can talk clearly about it to someone -> get in the habit of speaking to someone about what you learned from the book, while you am reading the book. It is best if this is your significant other or someone who also has interest in the subject.