Combine the lime juice, sugar and 1/2 cup water in a cocktail shaker; stir until the sugar dissolves. Add the tequila and orange liqueur. Rub the rims of 2 martini or margarita glasses with a lime wedge, then dip into coarse salt. Add ice cubes to the shaker, cover and shake for 10 to 15 seconds. Strain into the salt-rimmed glasses.