Slice a lime slice into a notch, then rub the wedge all the way around the glass rim. Dip the rim's edge into a salt dish (or for a festive look, useMargarita Salt).
Combine all the ingredients with 4 ice cubes in a cocktail shaker, and mix until chilled.
Pour the margarita through a strainer into the salted-rimmed glass. Serve the glass after adding ice to it. If desired, add lime wedges as a garnish.