Mix sugar and 1/4 teaspoon of the ginger on a small plate. Wet rims martini glasses with water. Dip rims of glasses into sugar mixture to lightly coat.
Fill cocktail shaker half full with ice. Add juices, tequila, orange-flavored liqueur and remaining 1 teaspoon ginger; shake until well mixed and chilled.
Strain into 2 beverage glasses. Garnish as desired. Serve immediately.