Gently brush away eraser filings, clumps or mold, or other debris from the pages. Use a butter knife or paring knife to pick away wax or other congealed fluids. Try first to remove pencil markings and other stains with a plastic eraser.
If the eraser does not fade the stain, gently use a very fine piece of sandpaper. Sandpaper should not be used on ink as it will also fade it. If the paper begins to grow diaphanous, stop immediately. If you have found mildew, begin by removing the clumps of mildew with a light brush. Kill the remaining mildew by either freezing the book or leaving it in sunlight. They can also be treated with chemicals.
Apply small amounts of rubber cement to grease stains or other waxy substances. Then, with your fingers, roll the cement over the pages. The cement will pick up the substances. Again, this method will remove ink from the page.
If you have found mildew, begin by removing the clumps of mildew with a light brush. Kill the remaining mildew by either freezing the book or leaving it in sunlight. They can also be treated with chemicals.
Remove dark mildew stains by applying lemon juice or diluted bleach. Alternately, you can use a fungicidal spray. Apply copper napthenate to prevent further mold growth.