Pour some salt (or sugar) onto a plate. Rim glasses by rubbing a lime wedge all around the outer edge of two margarita glasses, then roll or dip the rim of the glass into the salt until it's coated.
Then, fill a cocktail shaker with ice. Add the cranberry juice, tequila, triple sec and agave. Put the lid on and shake it hard!
Strain the margarita into your glasses and garnish with cranberries and a lime wedge or wheel.