Q: What’s the best way to clean the covers of a book?
A: When I worked at a retail bookstore, we always used Goo Gone. It’s an orange-based cleaner that easily removes sticker glue, dirt, grime, sticky residue, and many other markings. However, it can’t fix bends, scrapes, curls, tears, or other physical damage. And never use it on inside pages, because it may soak into the paper and leave a stain.
Whatever you do, don’t use regular household cleaners, which can damage a book cover. And don’t apply any cleaner directly to the cover – apply it to a soft cloth and then wipe the cover with the treated rag, then dry with an unexposed part of the cloth.
Before treating the cover with any kind of cleaner, including Goo Gone, try wiping the cover with a slightly dampened soft cloth first. It may take away the grime without having to apply anything at all.
I've said a couple of times here to use a soft cloth. Lest you think I'm just trying to be fashionable, keep in mind that rough textures can wear the cloth on a hard cover and the edges of paperback covers. Soft cotton works great.