If you have books that get wet and you need to dry the pages, do it as soon as you find out the pages are wet.
Get several rolls of heavy duty, industrial paper towels (the brown ones you find in many public restrooms, not the ones you have in the kitchen), a large fan, and a table or other work surface. Gently open the book, and place a paper towel between each page, and let the end of the towel hang out the side of the book. Don't force the towel down into the spine (the added thickness can break the spine), but make sure to cover most of the page. After you get paper towels between all the pages, open the book somewhere near the middle, lay it down on the table opened up as if you were reading, and let the fan gently blow over top of the book from across the room, not enough to move the pages, but enough to keep the air moving gently. After about 2 hours, go back and change ALL the paper towels, open the book to another set of pages, and do the same thing. Continue changing the paper towels and letting the air gently blow over the pages unitil the book is COMPLETELY dry. If it's not completely dry, you will likely end up with mildew in the book. Check the book periodically afterwards, to make sure there is no mildew started even if you think you got all the moisture out of the pages.