1. Chill your cocktail glass (the easiest way is to fill it with ice)
2. Add plenty of ice and the vermouth to your shaker/stirring glass and stir to make sure the ice is coated with vermouth, then use your strainer to pour away the excess
3. Add the Bombay Sapphire to the shaker/stirring glass and stir the mixture for about 30 seconds to chill and dilute
4. Strain into the chilled cocktail glass and garnish with either a twist of lemon peel or some green olives. If you're using olives, try to use ones that aren't oily