Look for marks. If it is made from sterling silver, it will be marked with a number 925. This is an indicator of the amount of solid silver used. The piece may also be inscribed with the words "Ster." "Sterling" or "Sterling Silver".
Perform the magnet test. Gold, silver and platinum are not magnetic, and will not attract a magnet. If the piece being tested holds a strong attraction to a magnet, it does not hold precious metal value.
Pick it up. Real silver isn't heavy and it isn't very light either. Compare the feel to that of a piece of known silver to know what the weight should be.