Run a lime around the rim of a rocks glass or a martini glass. Dip the edges of the glass in a platter of margarita salt.
Put a handful of ice in a cocktail shaker and add tequila, lime juice, lemon juice, orange juice, Grand Marnier and a agave nectar.If serving into a highball glass put ice in the glass before pouring. If serving in a martini glass pour straight up with no ice. Shake vigorously and strain into glass. Serve with a slice of lime.