Prep your glasses (this step is optional)- to salt the rim of your glass, run a lime wedge around the rim of your cocktail or margarita glass. Carefully dip into a shallow dis filled with coarse kosher salt and set aside.
Combine and shake. Add the tequila, lime juice, orange liqueur, and agave syrup to a cocktail shaker filled with ice. Seal and shake well until chilled.
Pour and serve on the rocks. Fill a margarita glass (or rocks glass) with ice and pour directly over the ice. Garnish with additional lime, if desired.