Run lime wedge around the outer rims of two rocks glasses and dip rims in salt. Set aside.

In cocktail shaker, combine tequila, Cointreau or orange liqueur, and lime juice. Fill with ice and shake until thoroughly chilled, about 15 seconds (the bottom of a metal shaker should frost over).

Fill glasses with fresh ice and strain margarita into both glasses. Garnish with lime wheels and serve.