You will forget half of what you read after 2 weeks and 90% after 2 months.
Some people think taking notes and reviewing them is boring or not necessary. This is simply not true. You will not retain what you learn from a book unless you get multiple repetitions of the information over time.
People tend to want the shiny new thing ("fresh" information) when really they would be better off reviewing what they have already read/forgotten. One you fully realize how much time you are wasting by not reviewing your notes (because you are forgetting so much of what you read) you will start to enjoy it. Most of the best ideas come from going back and collecting and synthesizing disparate notes and quotes from the books we have read.
Timothy Kenny, author of Accelerated learning for Entrepreneurs, suggests a simple process to retain information from reading:-
1. Consume your information
This means you underline your book, take notes from an audio or video course or collect the best posts from a forum into a word document or page in OneNote.
2. Boil it down
Transfer your highlights or underlines to a separate piece of paper so you have your own set of notes.
3. Boil it down again
Use a highlighter to go over your notes and find the most important pieces. You can circle chunks of text in your notes to start organizing them.
4. Create Your final product
These are only useful for certain types of information. Some books are more general facts/information and may not be worht the extra time investment if you only have a few pages of notes and not many actionable steps.
Use your chunked notes to create a mindmap. Stick to one page and fit in as much detail as you can.
B. Action List
Go through your notes and decide what you want to take action on. Prioritize the list and put it somewhere where you will look at it again, like the wall next to your computer.
Cut up your information into two sided notecards. You can do this by hand or digitally.
Tip: You can leave notes at any stage in the process and come back later. You can also skip or combine these steps depending on how aggressively you want to learn.
(End Game: The Ultimate Accelerated Learning System - Udemy)