2 oz of white rum (or Light Rum)
1/2 oz of Lime Juice
1 tsp of sugar
1 dash of cointreau orange liqueur (or orange liqueur)
Pour the rum, lime juice and Cointreau into a cocktail shaker half-filled with ice cubes. Shake well, and strain into a cocktail glass. Add sugar to taste, stir to dissolve, and serve.