Place the salt, sugar and lime zest in a shallow bowl and stir to combine completely.
Rub a lime wedge around the lip of each glass then roll in the salt, sugar and zest mixture.
Stir together all of the ingredients in a large pitcher. Pour the desired amount of margarita mix into a cocktail shaker filled with ice. Cover with the lid, and shake for about 30 seconds. Strain into chilled, rimmed cocktail glasses. Serve immediately.