Chill a martini glass in the freezer for at least 5 minutes.
Pour the gin and vermouth into a stainless-steel cocktail shaker or a chilled tumbler.
Place 8 to 10 ice cubes in the shaker or tumbler, stir vigorously for about 20 seconds with a long-handled spoon, and strain into the chilled martini glass.
How you finish off the martini is a matter of taste. A twist is the classiest way to go and yields the cleanest-tasting drink. An olive is the traditional garnish, and it looks cool. Take your pick.