Do it all in one shot. Unless you have an extortionate amount of books or your books are in dozens of places around the house, this is something you should be able to take care of in an afternoon. If you do have either of the two situations, break it down and do it one room at a time.
1. Sort and Segregate
The books you want to lose are things you do not read and will not need in the future. You need a donation/sell box (easiest if you simply decide donation OR sell, not both because that will slow the process down). For each book go through a series of questions: Will you read it in the future? Do you need it as a work/personal reference? Do you have someone specific in mind to give it to? Do not think about how much you spent on it or how you had meant to read it, only think about the future use.
Find one (and only one) place to get rid of your books. There are numerous places to donate your books. Many nieghborhoods have donation boxes or call you local library about donation opportunities. When it comes to selling, look for neighborhood resale shops (we use Half Price Books). Although there may be ways to make more money by selling your books individually (example on Amazon), the point of the article is to declutter, not to maximize profits. If you simply get rid of everything at one stop, it is gone with no worries.
3. Lose the Guilt. Feel ok with keeping some. So you kept some books you are not sure when you are going to read again. So you kept some books out of sentimentality. The point is you should not look at your shelf and see anything you know you will not read again. You can always repeat this process again in a few months or a year. Books are not trophies to display they are valuable resources for reference, intellectual stimulation, and entertainment.
Bonus Step: Check out Local Library and Get Library Card
This step will help you from accumulating more books you may only have a passing interest with. Whenever I go to the library, I check out 8-10 books on the same topic (and get a crazy look from my husband). This allows me to go home, look at the books at my leisure, read the valuable parts of the best books, and return them all when I am finished. Of course, one needs to be careful not to lose them within the house.
As you may be able to guess, this was my little project yesterday. Whenever B and I move, we always seem to leave stuff in boxes for months (often books). We also have tons of books left over from our collective two degrees in history. However, I have need for many of them at my work and they represent a significant personal interest of ours. I think have a lot of books in our home will always be a part of our life, with period trimming and decluttering.