Cut a notch in a lime wedge, then run the lime around the rim of a glass. Dip the edge of the rim into a plate of salt.
Place all ingredients in a cocktail shaker with 4 ice cubes and shake until cold.
Strain the margarita into the glass with the salted rim. Fill the glass with ice and serve.
For a margarita pitcher (8 servings): Place 1 ½ cups tequila, 1 cup Cointreau or Triple Sec, and ¾ cup lime juice in a pitcher. Add 3 handfuls ice and stir until cold. Pour into the prepared glasses.
Notes
For a spicy variation, add 3 to 4 jalapeno pepper slices to the cocktail shaker, or go to Jalapeno Margarita.
For a smoky variation, replace half the tequila with Mezcal, or go to Mezcal Margarita.