Add the tequila, Grand Marnier, lime juice, orange juice, (water if you are using it) and a handful of ice to a cocktail shaker.
Put on the top and shake vigorously, about 15-30 seconds.
For a salted rim, run a lime slice along the edge of the serving glass. Swirl the moistened rim into a small plate of coarse sea salt. Add ice to the glass.
Strain the margarita into the serving glass. Garnish with additional lime slices if desired. Enjoy!
