Summarize this article:

Position your paperback and small hardback book standing up. Line it up next to books that are approximately the same size to prevent it from warping out of shape. Make sure that your books aren't leaning, and use book ends if necessary to keep them straight. If your book is too large to store upright, lie it flat with no more than two other books stacked on top of it. UV rays from the sun can cause book jackets and covers to fade over time. This damage is permanent and it will devalue expensive or rare books. Place bookshelves in a shady corner of the room whenever possible. If you can't store your book out of the sun and wish to protect it from fading, purchase a UV-resistant cover for it online or in a book store. As a general rule, try to keep your book in a room that is 70F (21C) or cooler. Make sure that the room is not damp or humid, which may encourage mold to grow. Keep your book away from heaters or heating vents, as excessive heat can cause your book to deteriorate faster.

Summary:
Position your book upright with similarly sized books. Keep your book out of direct sunlight. Store your book at room temperature and keep it dry.