Place some salt on a small plate. Rub rim of an old-fashioned or rocks glass with lime wheel (reserve for serving); dip in salt.
Combine watermelon juice, tequila, and lime juice in a cocktail shaker.
Fill shaker with ice, cover, and shake vigorously until outside of shaker is very cold, about 20 seconds.
Pour contents into prepared glass. Garnish with reserved lime wheel, or basil and blueberries.