Cleaning old books and their aging paper can present a conundrum. There are many ways to clean books and ephemera, but the more effective the cleaner, the more abrasive it may be, and the greater the risk that cleaning will cause damage. Weigh the need for cleaning against the stability of the book and what it’s made of; always test, especially when colors or fabrics are involved.
If you can, enlist a helper so that whilst one person transfers a wedge of books onto a Table to be cleaned, the other cleans the empty shelf. Incidentally, it’s worth the extra work of cleaning your books away from the bookcase. That way you know the same dust you wipe off now won’t just settle back on the books later.