Make the citrus sugar: In a small bowl, combine the sugar, lime zest, and orange zest. Mix well.
Rim the glass: Moisten the rim of a chilled martini glass with a lime wedge. Spread the citrus sugar on a small plate and dip the rim of the glass into the sugar.
Combine ingredients: In a shaker filled with ice, combine vodka, Cointreau, cranberry juice, and lime juice.
Shake: Shake well until thoroughly chilled.
Strain: Strain into the prepared martini glass.
Garnish: Garnish with an orange twist or fresh cranberries.