One common problem of storing books is that covers often stick together between books. While this is often merely an annoyance, when the covers stick together too firmly, they can rip apart once the books are finally separated. Avoid this problem by placing pieces of paper between the books. Be careful not to use newspaper; the print from newspaper can transfer to the book over time, causing damage.
The most potentially dangerous problem inherent in storing books is that, when combined with humidity, they can attract mold spores, which pose a health risk. You can avoid this problem by ensuring that you store your books in a climate-controlled environment. Although you might not have this option if you are storing the books at home, if you are storing the books in an external storage facility, ask if this option is available at an extra cost. The extra cost is worth it, as it will help save your books from mold.
Seal your books in plastic bags to ensure that mold cannot transfer to them. One small plastic bag per book is ideal, although one large plastic bag (sealed tightly) will also suffice. The goal with the plastic bags is to ensure that the mold spores cannot land on books to begin with. Combined with a climate-controlled environment, plastic bags can go a long way towards protecting your books from mold.
When packing the books, place the largest, heaviest books on the bottom. This will ensure that the heavy books do not bend or warp the lighter books. Fill the boxes as completely as possible and see that little space remains in between them. This will prevent the books from shifting, potentially bending or warping the books. Always avoid storing the books by resting them on the spine. This method will permanently damage the book.