Salt the rim of the glass (optional): Rub a lime wedge around the rim of a rocks glass. Fill a small plate with coarse salt. Dip the glass into the salt to coat the rim. Fill with ice.

Place the tequila, orange liqueur, lime juice, and agave in a cocktail shaker with ice. Shake and strain into the glass. Taste and stir in more agave nectar, if desired. Garnish with lime slices and serve.