what Fernie said ^^^^^^ and also the Goddards liquid one is good
Cleaning and care of silver
Whatever product you use to clean your silver will inevitably remove a very slight layer. Therefore, it is important to use the least abrasive materials, such as silver foam or liquid polish and to make sure that you buy the long-term variety.
Silver is a very soft metal and scratches very easily. Never use a metal polish intended for copper or brass and never use wire wool or an abrasive kitchen pad.
http://www.antique-silver.com/info/advice.htm