Research this classic cocktail and you'll find at least a couple differing recipes.
Most specs call for rye, whereas I'm using bourbon in this drink. Other recipes use less Campari & Sweet Vermouth, such as 3/4 oz each instead of the full ounce of each that I use here. Research the drink, check the specs, try 'em out and tailor to your liking.
1.5 oz bourbon
1 oz Campari
1 oz sweet vermouth
Stir all the ingredients over ice and strain into a rocks glass filled with fresh ice, or into a chilled cocktail glass. Garnish with an orange peel or lemon peel.