Storing your jewellery in separate airtight plastic bags (preferably with anti-tarnish strips inside) is a great preventative measure against tarnishing!
If you wear your jewellery often, the oils in our skin keeps the silver looking shiny. However, if it is exposed to household chemicals, chlorine, perspiration, cosmetic products or perfumes it will cause corrosion and tarnish.
If it does become tarnished, then it can easily be cleaned either with a silver cleaning cloth or just using warm water and a mild dishwashing detergent. Rub gently, particularly with silver plated items, as excessive polishing can possibly remove the plating.
If you feel a deeper clean is needed then you can do this at home by lining a small bowl with aluminium foil and placing your pieces on the foil. Then cover the jewellery with hot water and add a tablespoon each of baking soda and salt. Gently stir so the soda and salt dissolve. Leave the jewellery in the solution and after 5-10 minutes the tarnish should have disappeared. Remove the pieces with metal tongs or drain into a colander. Rinse in water and gently dry with a soft cloth.