Avoid exposure to household cleaners and chemicals that can damage your jewelry. Remove your jewelry before dealing with chemicals. Pearls and other porous stones can obviously be damaged by the chemicals, but even karat gold can be discolored by chemical exposure (chlorine, for example), even something like a soak in a hot tub. Use rubbing alcohol to remove grease from karat gold. Remove earrings when you have your hair done, especially if you are having it colored.
Apply all of your cosmetics, make-up, hair spray, and perfume before putting on your jewelry. Remove bracelets and rings before applying hand lotions and creams. Remember that you should remove your jewelry before working in the garden or engaging in other physical labor, exercising, swimming, bathing, etc.
Finally, please don’t just toss your jewelry into a jewelry box or drawer - your pieces will scratch each other. Jewelry often comes in a protective bag or box and you should store your jewelry in these boxes and bags or flat in a plastic bag in a clean dark dry place. Store pearls in soft bags away from other jewelry which might scratch the pearl’s surface. Store your silver jewelry in tarnish resistant bags.