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 syrup or simple syrup.
Shake vigorously for about 15 seconds.
Pour the blueberry margarita over ice and garnish with a sprig of fresh mint, lime slices, and a handful of fresh blueberries.