Blot a damp or wet book dry as thoroughly as possible with a soft cloth or paper towels, and leave the book in the open but not in direct sunlight. Blot pages instead of rubbing, as older inks may smear under pressure.
Freeze a book that you cannot immediately dry. While freezing will not eliminate mildew, it will temporarily halt its growth and give you time to prepare any drying tables or cloths you might need to deal with moisture.
Place the book beneath, but not fully within, the stream of air from a portable fan. Air should move across the top of the book's open pages rather than hitting the page directly. Think of how you would blow across the surface of a spoonful of soup to cool it instead of blowing directly at the spoon and possibly splashing the soup.
Turn the pages periodically to expose more of the book's damp surfaces to the air.
Close the fully dried book and store it as usual for a week or so, and later pull it out to ensure that it has developed no musty odors or visible mildew.
Dust books regularly to prevent spores from taking root on their covers or between their pages. Mildew and mold spores comprise a portion of household dust and are impossible to eradicate completely. However, regular dusting will disrupt individual spore growth and slow mildew formation.
Store your books in well-ventilated areas that have gentle air circulation. Books that you box and store in the basement or on the floor of a closet have a greater risk of developing mildew than books on open bookshelves.
Keep the temperature at which you store books as uniform as possible throughout the year. An air conditioner is one of the best mildew-prevention tools at your disposal as it lowers the ambient humidity surrounding books.
Place packages of commercial desiccants such as silica gel, activated charcoal or kaolinite clay in hidden corners of bookcases and atop books in boxes. Desiccants absorb moisture from the air more readily than paper does. Where desiccants maintain an arid atmosphere, mildew cannot grow.
Shelve books against interior walls, away from windows and at least a few inches from the floor. While the overall humidity of the room might be less than 50 percent, localized humidity on floors and uninsulated exterior walls may become significantly higher and allow mildew growth.