Tarnish is caused by a chemical reaction between the silver and sulfur, or sulfur-containing substances such as air, water, wool, felt, rubber etc. You cannot wash tarnished silverware in soap and water to make it shiny again . . . it has to be polished. I read that silverware should not be wrapped in newspaper, since the ink is acidic and can harm your silver. Rubber bands should also not be used to hold your silverware together, as rubber bands contain sulfur which causes excessive tarnishing and other damage to the surface of the silver.
Silverware should not be stored in plastic bags either, since these bags can trap moisture within them which can accelerate tarnishing, and also cause pitting. Silverware should be kept in an area without high humidity and out of high heat such as in a chest, draw, or china cabinet. They may also be stored in flannel treated bags and cloth to help retard tarnishing.