Take a cocktail shaker filled with ice and pour in the tequila, Grand Marnier, fresh squeezed lime juice, lemon juice, orange juice, and 1 ounce agave nectar.
Close shaker and shake vigorously.
Taste it and add another ounce of agave nectar if it's too tart.
Shake to incorporate the extra agave.
If salting the rim, run the 1/2 orange around the rim of the glass to wet it. Then dip the glass upside down in a small saucer of kosher coarse salt.
Fill glass with ice and pour cocktail over ice.