Squeeze lime and orange juices into glass measuring cup. (I measure using the metric side.)
Add tequila, Cointreau, and agave nectar. Stir well. Taste and add more agave nectar to taste if desired.
To salt glass, rub cut lime around outer edge of the rim, coating the top 1/2″ well with lime juice. Pour about a teaspoon of salt into the palm of your hand, and roll outer edge of glass in salt until coated.