Mix the cocktail: In a mixing glass filled 2/3 with ice, pour in the gin, Campari, and sweet vermouth. Stir for 20 seconds to chill and mix, and then strain into a rocks glass with fresh ice.
Serve: Garnish with the orange peel and serve.
Notes
If you want to go the extra mile, chill your serving glass. Store for a few hours in your freezer, or fill with ice water and dump before adding the cocktail.
You can serve a Negroni straight up in a coupe glass, or over ice in a rocks glass.
Serve over ice if you want something to sip on for a while, or serve up for a stronger drink.