From The Boys’ and Girls’ Little Book of Alcohol, available at amazon, iTunes, and barnesandnoble.com:
The Negroni (original version)
1 oz. high-enough quality gin (most of the flavor will be overpowered by the other ingredients)
1 oz. Campari
3/4 oz. sweet vermouth
Mix the three liquors in a shaker filled with ice. Shake and then strain into a pre-chilled martini glass.
The Negroni (my way)
1 part better gin—there’s more of it proportionally, so you taste it more clearly
1 part Campari
A splash of sweet vermouth
Follow the same mixing instructions as above. But I like to taste gin and Campari more than sweet vermouth, so I drastically reduce the vermouth. Try the original recipe first, then play around.