Sterling silver can tarnish over time if exposed to air. The optimal way to bring back its' shine is with a Sunshine or similar polishing cloth, by gently polishing the surface.
14 karat gold fill and 14 karat gold do not have the same propensity to tarnish. However, if jewelry made with these metals does become soiled, soak in a solution of a few drops of mild dishwashing liquid mixed with two cups of warm water and gently clean with a soft brush.
Freshwater pearls are more fragile than other gemstones, so to keep them beautiful you should put them on after you've applied your make up or perfume, never clean them with solutions containing ammonia, harsh detergents or abrasives, do not use an ultrasonic cleaner, do not soak them, and keep them in a soft bag to avoid them getting scratched. Freshwater pearls can be cleaned by gently wiping with a soft, lint-free cloth. If they become damp, allow pearls to air dry.