Avoid placing antique books on a wooden bookshelf. Metal shelving with a baked enamel finish is preferable. If you only have wood shelving, seal it (with a water-based aliphatic urethane) to prevent the wood's natural acids from deteriorating the books. If your wood shelving is old, it should be dried out enough to be vapor-free and safe for storage. Keep in mind, regardless of age, that oak is the most acidic wood and the least favorable choice for shelving.
For fragile antique books, place them in individual boxes, constructed of acid-free materials. Do not use slipcases (containers that slide onto the book). Slipcases leave the spine exposed, not appropriately protecting the book from usage wear. If your book has an original dust jacket, keep it. The jacket increases the value of the book. You should remove an original dust jacket only if you cannot control the book's environment (poor temperature and relative humidity management may cause mold to grow between the jacket and the book).
Place your books to stand upright or lie flat; they should never slouch. Position large books (more than 18 inches tall or with a spine wider than 3 inches) to lie flat. If you set a large book upright, the binding may fail, resulting in a warped cover, weakened spine and separated pages. Don't stack more than three large books on top of each other.
For normal- to small-sized antique books, don't pack them too tightly on a shelf. Arrange the books to sit close enough to support each other, yet loose enough to remove easily.
Only use a bookend to support your collection if it's tall enough to keep a book from leaning over it. Similarly, don't place tall books next to short books; if you do, the taller books will deform with time.
Create a stable environment for your antique books by keeping the temperature fixed (between 65 to 70 degrees Fahrenheit), maintaining the relative humidity and limiting exposure to light and dirt.
Manage the relative humidity level to stay between 40 to 50 percent. Too low of a level weakens a book's pages, and too high encourages mold and mildew growth (your collection should be well ventilated to also help prevent mold and mildew).
Protect antique books from ultraviolet and visible lights. Ultraviolet breaks down paper and cloth fibers, while visible light fades colors and damages leather. If you use fluorescent lights, place ultraviolet filters over them. Block sunshine and keep any light around the books dim.
If you live in a high air-pollution area, purchase high-efficiency filters for your ventilation system. Portable air cleaners also can be an option, if needed.