When people begin to entertain the idea of creating an in-home library it is important to plan ahead depending on the type of a library is actually desired. Library design must suit the function! There are three major types, as far as I can tell.
1. Display library.
If you have an existing collection of rare books and first editions this is probably the type of library you are thinking of. It is a much more difficult task to start a display library if you do not already possess some considerable bibliophile treasures. In many cases, books in a display library are not meant to ever be read or consulted. These books are nothing but investment, and to protect this investment you need to consider adequate security measures, as well as storage facilities with temperature and humidity control. You cannot replace your display library should anything happen to it!
2. Decorative library
If you want to show off books that do not hold any intrinsic value, but are simply beautifully crafted, your task is somewhat less burdensome. No need to worry too much about proper storage and security. Still, try to treat your books as well as you can. But it is important to make the distinction between decorative and display libraries, in my opinion. There are some resources on home library books used in decorating, by the way.
3. Working house library
The most useful kind of home library, in my humble opinion. Usually, people who need to consult books on a regular basis turn their entire living spaces into libraries. As a friend of mine put it, "I live in a giant bookcase." This type is at its best is a proper research library at home.
4. Mixed libraries
You can certainly mix the three main library types. Just be sure to separate the books, using separate bookcases for various types of books. You can also have, for instance, a display library next to the dining room and a working library upstairs etc.