Pearls are not as hard as mineral gemstones, and they are organic. Therefore you need to treat them a little differently than your other jewelries.

The best way to keep your pearls beautiful is by wearing them. Your body's natural oils can keep pearls moist and lustrous. When dressing, put on pearls only after applying hairspray, cosmetics, perfume or other potentially harmful substances that might stain them. 

Wipe your pearls with a soft, lint-free cloth as soon as you take them off. The cloth can be dampened with water or it can be dry. If damp, allow the pearls to air dry before putting them away.
Even cultured pearls with thicker coatings are more fragile than most other gemstones. To prevent chipping, pearl jewelry should be stored in soft cloth, away from other harder jewels. Dirty pearls can be cleaned with a mild soap and water solution. Never clean your pearls with solutions that contain ammonia or harsh detergents.

Your fine pearl necklaces should be restrung periodically so that you're sure the silk or nylon cord holding them is in good shape. It is recommended that you restring pearls every few years as strings can wear down and break if not maintained.