Gather all your ingredients.
Place the sugar on a small plate.
Pour lemon juice onto a separate small plate.
Dip the rim of your martini glass in the lemon juice, then coat the rim with sugar from the plate.
Fill your cocktail shaker with ice cubes.
Add the vodka, black cherry juice, grapefruit juice, and agave nectar to the shaker.
Cover the shaker with its lid and shake vigorously for about 10 seconds until the mixture is well-chilled.
Strain the mixture into your prepared martini glass.