Wet sugar cube with bitters and a dash of soda or water in an old fashioned glass, muddle, add ice and whiskey, stir to dissolve thoroughly, garnish
Some prefer a fruity garnish, including an orange slice, lemon twist, and 2 maraschino cherries. Some top with a splash of soda. Perhaps more so than any other cocktail, the Old Fashioned may be endlessly varied by using different spirits, or by adding a dash of curacao, absinthe, or other liqueur. Some would argue that these latter additions make it an "Improved" cocktail.
The original cock-tail, a combination of whiskey, sugar, bitters, and ice.
Gary Regan, The Joy of Mixology. http://en.wikipedia.org/wiki/Old_fashioned_cocktail