Today I've realized the best piece of advice I should be giving is simple.
Build floor to ceiling and wall to wall bookshelves.
Yes, you read that right. Pick a room and a wall or two, measure, and then either shop at Ikea or, if your the handy type, the lumber store.
Doing anything less and you'll only regret it* as the years progress and the books pile higher. At which time, you'll pick a room, measure a wall or two and head to Ikea.
|Sure your shelves may start out looking like there is plenty of room. . .|
|But before you know it, they'll look like this and you'll wonder which other wall would be good for more shelves|
*Speaking from experience and a room full of piles until the new shelves are able to be put it into place.