Chill your glass.
Place an old-fashioned or rocks glass in the freezer for a few minutes while you gather ingredients.
Mix the drink.
In a mixing glass or directly in the serving glass, add gin, Campari, and sweet vermouth in equal parts.
Add ice.
Fill the glass with large ice cubes (they melt slower and keep the drink from watering down).
Stir gently.
Use a bar spoon to stir for about 20–30 seconds until the mixture is well chilled and slightly diluted. The drink should look glossy, not cloudy.
Garnish and serve.
Express the oils from an orange peel by holding it over the glass and giving it a gentle twist, then drop it in, or garnish with a simple orange slice for a classic finish. Enjoy immediately.