Lightly charring the fruit for this cocktail gives it an unexpected smoky edge that all your guests will love.
1. Set grill to high. Place the sugar in a small, shallow dish. Cut the limes, lemons, and oranges in half. Dip cut sides in sugar.
2. Place citrus on grill cut sides down and cook 2 min., until dark grill marks appear. Remove citrus from grill and let cool slightly. Into a medium liquid measuring cup, squeeze juice from citrus, reserving 2 squeezed lime halves. Strain juice into a pitcher. Stir in the tequila, triple sec, and agave nectar.
3. Place the salt in another small shallow dish. Run reserved squeezed lime halves along rims of 4 small margarita glasses to moisten. Dip rims of glasses in salt. Add ice to glasses. Divide margarita among glasses.