Rim a margarita glass with salt if desired. Fill with ice and set aside.
Add tequila, blood orange juice, lime juice, triple sec, and agave nectar to a cocktail shaker.
Fill the shaker with ice and shake vigorously for 10-15 seconds.
Double strain the mixture through both strainers into the prepared glass.
Garnish with a blood orange wheel.
Notes
Blood oranges work best when they're in season from December through May. Store-bought juice can work as a substitute.The drink should be served right away while cold and fresh.Regular oranges can replace blood oranges, though the color and flavor will be different.For a spicy version, add 2-3 thin jalapeño slices to the shaker before mixing.