There are, in my experience, only two sorts of people. The first have very few books and little or no interest in them. The second, and I'm talking to these people, have too many and keep acquiring more.
One day you have to face the fact that some of them have to go but books are not ordinary stuff and getting rid of them is emotional as well as a practical task.
Here are my suggestions for that task.
1) First remove duplicates. I know that sounds obvious, but many of us have them.
2) Sort through the rest and decide which ones must go. Be ruthless. In the unlikely circumstance that you decide that you got rid of a book that you wanted, you will find that very few modern books cannot be borrowed from your library or bought online for relatively small sums of money. For example, how often do you re-read a novel? Be honest! Are you keeping your favourites so your children can read them? How likely is that? If you have a fine collection of romances and no daughters, they are very likely never to be read again, so consider rehoming them (I prefer the term rehoming to disposing). Are you ever going to take up pyrography, surgery, go on that 1980s fad diet? Please insert the subject of your own white elephant non-fiction books into that sentence. Free yourself from the guilt of not doing these things by removing the books from your shelves.
Now you have a heap of books to leave (and some space on your bookshelves!). I find it disheartening to think of these books languishing on a charity shop shelf waiting for the one person who wants them so what follows is my strategy for minimising that.
What can you do with them?
1) Give away to people you know
3) Give to charity
4) Swap for books you want
Point 1 is easy - you know who has small daughters who will love the Flower Fairy books your sons despise or who has sons who want the Action Man books you loved as a boy but which your daughters ignore.
My next post will go into more detail on how to do the others, giving you space, possibly some money and a smug feeling of having done something useful.