As with many cleaning tasks, routine maintenance is key to keeping your library relatively dust-free. Clean bookshelves by vacuuming, with lambswool dusters, microfiber, dampened or treated dusting cloths. However, avoid using damp or treated cloths on the books themselves, since moisture and chemicals can damage pages, covers and bindings.
Gently vacuum dust off books using a brush attachment and a crevice tool. Regularly vacuum the area around bookshelves to minimize the amount of dust that can settle on the books.
Rare volumes or antiquities on your bookshelves should be cleaned by professionals.
Creased pages can be partially restored with a steam iron set on low heat; use sheets of paper on both sides to protect both the creased page and adjacent leaves.
Clean leather binders with a leather cleaner and restorer. Dressings such as saddle soap or lanolin are no longer recommended for cleaning leather covers since such treatments can soak into adjacent volumes, and may promote the growth of mold.
Smudges or stains on book covers can sometimes be removed by gently applying a pencil eraser. If the smudge remains, and the surface permits, use a cloth dampened with water, or add a small amount of mild soap, damp-wipe, and then blot dry.
Remove dried mildew spots by vacuuming, followed by putting the book in direct sunlight for no more than 30 minutes at a time. Heavily mildewed volumes should be removed from your collection to prevent mildew from spreading to other books.
The best way to rid books of insect infestations is by freezing them. Place the book in a plastic bag first and leave it in the freezer for a couple of days, then shake out or vacuum out the carcasses. To prevent future invasions, place cloves or bay leaves behind the books. To make room for this, pull books forward to the edges of the shelves. This will mean less shelf dusting in the future, too!
References:
Don Aslett, The Cleaning Encyclopedia: Your A to Z Illustrated Guide to Cleaning Like the Pros
Jeff Bredenberg, editor, Clean It Fast, Clean It Right: The Ultimate Guide to Making Everything You Own Sparkle & Shine
Consumer Reports editors in How to Clean and Care for Practically Anything.