Do not wear in water, or during any strenuous activity. Sterling silver can tarnish like any other metal. Other ways to clean is silver cleaner or organically you can use -
Toothpaste: Squeeze a dab of organic toothpaste on a piece of cloth or flannel, and rub onto silver.
Baking soda and water:Mix baking soda and water to make a paste, then rub silver with it.
Water/baking soda/aluminum foil:Place jewelry in an aluminum pan or a baking dish lined with foil. Liberally sprinkle baking soda over the pieces. Pour boiling water over top and allow it to soak for about 15 minutes. The tarnish will magically appear on the foil rather than the silver.