To rim your glass, you'll need to combine the sugar and dried cranberries on a small plate. Wet the rim of your glass with water and place it upside down on your sugar plate. Use your fingers to gently press the sugar and cranberry bits onto the edge of your glass. Turn the glass upright and allow it to dry for a minute or so.
In a measuring cup or another container (something with a spout will be less messy) stir together tequila, triple sec, and cranberry juice.
Carefully place some ice in your rimmed glass and pour your cocktail over the ice. Garnish with a wedge of lime to squeeze in just before drinking.