Old books are a lovely link to the past, but a rather fragile one. Dust, small smudges, and pencil marks are fairly easy to remove. More serious damage such as that caused by insects, acid or moisture is more difficult but not impossible to repair. If you are dealing with an antique, you may prefer to leave it to a professional.
Steps
Method 1 of 2: Remove Dirt, Stains, and Odors

Step 1. Blow the dust off the edges
Hold the book closed and blow the dust on each edge of the pages. Remove trickier dust with a clean, dry brush or a new toothbrush.

Step 2. Remove smudges and pencil marks with an artist eraser
This is softer than a rubber eraser, but you should still use it very carefully to avoid tearing the paper. Work with the artist eraser in one direction.

Step 3. Remove complex residue with Absorene Book Cleaner
This is a smooth, moldable paste that will remove dirt and smoke residue from pages and fabric bindings. Just gently glide it over the surface to collect dirt.

Step 4. Clean leather bound volumes
Apply some clear shoe polish or cleaning polish with a soft cloth. Test one corner of the book first to make sure it doesn't remove the ink. Wipe off the polish with a clean cloth after you've removed the dirt.

Step 5. Clean cloth bindings
Gently clean your cloth bindings with an artist's eraser. Excess dirt may require a cloth dampened with fabric softener, but be aware that doing so increases the risk of damage or mold. Make sure the book is completely dry before storing.

Step 6. Wipe with a slightly damp cloth as a last resort
This is only recommended for paper covers and waterproof dust covers. You can also try it when the dirt is particularly difficult to remove, if you accept the risk of additional damage. Here's how to minimize that risk:
- Take a microfiber or other lint-free cloth.
- Rinse the cloth in very hot water, then wring it out very well.
- Wrap a dry towel around the cloth and wring it out again. Remove the cloth, which should now be just barely damp.
- Gently wipe the dirt off the cover and very lightly from the edges of the pages as well.
- Wipe with a dry cloth immediately afterwards.

Step 7. Clean up sticky residue
Label adhesive or other residue responds well to a little baby or cooking oil on a cotton ball. Press firmly and rub until the glue lifts. Remove the oil with a clean piece of cotton.
Oil can stain some materials. So first test in a corner

Step 8. Absorb odors
If the book smells musty, put it in a container with something that can absorb odors and moisture. Try a sock filled with rice or cat litter, or place the book on a newspaper dusted with talcum powder.
Sunlight will make this more effective. A shade cloth will help reduce color fading
Method 2 of 2: Repair Serious Damage

Step 1. Dry wet books
Books that have been subjected to water damage, either by immersion or spillage, should be dried slowly and carefully. A ventilated storage closet is ideal, but you can use a surface near a heater or a window through which the sun enters. Open the book to allow air to circulate and carefully turn a few pages at regular intervals to prevent sticking. Once dry, place it under several books that press down on it to flatten the pages and restore their appearance.
Even if you are tempted to do so, do not use a hair dryer or fan. This can easily damage the pages and cause them to loosen from the spine

Step 2. Freeze the books that have been affected by pests
If the book is full of tiny holes, or if pieces of paper come off when moved, it could be infested with mites or other paper-eating pests. To prevent further damage, seal the book in a bag and remove the air from it. Place the bag in the freezer for several weeks to kill insects and eggs.

Step 3. Check for signs of mold
Mold often has a strong musty odor. Any book with warped, wet binding, sticking pages, or obvious water damage also indicates a risk of mold. Unfortunately, mold damage is extremely difficult to repair without hiring a professional. Store the book in a warm, dry place to minimize further damage.
If you see white or fuzzy gray mold on the pages, wipe it off carefully with a soft cloth

Step 4. Repair the binding of the book
In severe cases, you can repair-a-book-binding or bind-or-reinforce-a-book. While it is not difficult with practice, it is best not to try it with rare or highly valuable books.

Step 5. Seek professional advice
Any bookseller or seller of rare books should be able to advise you on more specialized cases. If you have a very valuable or old book, consider hiring a professional archivist to do the repairs.