Here is our journey of decluttering books for the second time in one week. I tried my old method of leaving it on the shelf and thinking what-if I need it in the future and you can guess what happened... I got rid of very few books. Not 7 days later we went through our books again and discarded 6 milk crates of carefully placed books finally utilizing my Tetris skills. We may not want or need them anymore but someone, somewhere may and I don't want to treat them badly. They have served us well. We now know what we will and won't read and will be wasting less money in the future. We also learned a lot about ourselves during and after this discard.
How to declutter books the effective way
Take all the books (even the ones you know you want for sure) off the shelf and place them on the floor or a table (if they can all fit in one big pile or area). It is important to be able to see them all in one location to really understand how many you have. Choose a book you love and one you know you don't want anymore. Then use these 2 books to gauge your responses each time you pick up a book. Pick up books one by one making individual decisions for each book. Make a discard pile, a keep pile and a pending pile to address after going through everything else.
We took all our books to a local book store called Chamblin Bookmine. They take books and give store credit.