A pretty standard recipe uses 3:2:1 ratios (1.5 oz tequila, 1 oz orange liqueur, and 0.5 oz fresh lime juice). However, below is this is the mix we prefer. You can to tweak it to your own preferences.

2 oz freshly squeezed lime juice
1 oz tequila
1 oz rum
1/2 oz orange juice
1/2 oz simple syrup (or agave nectar)

Mix the ingredients above, and pour into a glass, over ice.

Margarita Mocktail (alcohol-free)

2 oz freshly squeezed lime juice
1 oz orange juice
1 oz water
1/2 tsp ginger shot (store-bought or home made)
1 tsp simple syrup (or agave nectar)
3-6 drops angostura bitters (optional)

Mix the ingredients above and pour into a glass over ice. (See notes above on rimming the glass.)

Notes and Options

Rimming the glass:
Fill a shallow bowl or plate with salt (or sugar). Run a lime slice around the rim of the glasses. Dip the rim in the salt (or sugar) until it is covered with your desired amount.

Simple Syrup Recipe:
Mix equal parts water and white sugar and heat until the sugar is dissolved.

Blender Option:
Blend ingredients in a blender with plenty of ice to make a slushie drink.

Mexican Bulldog:
The slushie option can be served with beer (or alcohol-free beer) to make a “Mexican Bulldog”.

Spritzer Option:
Add sparkling water to the regular, or the slushie version.

Egg White Option:
For a more professional-tasting margarita (smoother taste and slight foam), shake the ingredients along with 1 Tbsp of egg white and some ice in a cocktail shaker. Or you can give it a very quick whirl in the blender. This works for the alcohol, and the alcohol-free version.
(You can buy a carton of pasteurized egg whites and freeze them in 1 Tbsp portions.)