Ingredients: bourbon, red vermouth, a maraschino cherry.
Shake one jigger each of bourbon and vermouth with ice and strain into a chilled cocktail glass. Or serve on the rocks in an old fashioned glass. In either case, garnish with a cherry. The flavor is much improved if the manhattan is allowed to stand for two minutes in the fridge.
With scotch instead of bourbon, this is a Rob Roy.
My grandfather's tips were to add a few drops of the maraschino cherry liquid and a dash of grenadine. Some add angostura or other bitters; this is not successful, in my opinion, although check out the brilliant manhattan made by bar manager "Jennifer" at Lucky Strike in (where else?) Manhattan (212-941-0479).