I adapted this recipe I found on Liquor.com to my preferences, which makes it more sour and less sweet.
Salt on the rim, lime slice
Margarita glass
Rub the rim of the glass with the lime slice to make the salt stick to it. Shake the other ingredients with ice, then carefully pour into the glass (taking care not to dislodge any salt). Garnish and serve over ice.
Source: Liquor.com