Fill a cocktail shaker halfway with ice. Add 4 oz blueberry juice, ¾ oz lime juice, 1.5 oz tequila, and ½ oz Cointreau to the ice-filled shaker. Pour in ½ oz agave or simple syrup.
Shake for about 15 seconds. Pour blueberry margarita over ice and garnish with a sprig of fresh mint, a few slices of lime, and some fresh blueberries.
