1-1/2 Jiggers 100% agave Tequila
1 Jigger Orange Liqueur - (Cointreau or a basic Triple Sec)
1/2 Jigger fresh lime juice ( Juice 1/2 lime )
1/4 cup crushed or small cubed ice
Shake it all up in a cocktail shaker, and pour into a salt rimmed glass.
That's it! All traditional margarita recipes are very close to this formula. It really is that simple and for a true Traditional Margarita you should stick to these basic ingredients. When a Margarita is made correctly with the right ingredients it can be magical.
Apparently Margaret Sames used Cointreau in her "Original Margarita" and for a true Margarita stick with this or a basic Triple Sec. However, many get exotic with different liqueurs derived from oranges and yet other fruits and flavors. The "Baja" Margarita is usually made with a liqueur derived from the Damiana flower. Agavero is a great Tequila and Damiana based liqueur that makes a very nice Margarita. There are also many Mexican brands of Almond/Tequila liqueurs that can be interesting options. It is fun to experiment and the possibilities are endless.
A Note About Limes:
The experts tell you to use fresh lime juice when possible and I agree, however the limes we get in the US can often be quite bitter. This is probably the primary reason that many who try to replicate the perfect margarita at home are left disappointed. It simply is the limes. The best option is to try and find Mexican Limes (Limón, Limónes). The smaller "Key Limes" are sometimes called Mexican limes and in fact, probably even grown in Mexico. These are a good option but you can also visit a Mexican grocery and look for Limónes which from my observations are usually a little bigger than key limes but not near the huge size we see in US varieties. Mexican limes are normally sweet enough to be eaten alone and you can't say that about all limes. This is why the choice of limes is so important for a good Margarita.
If you can't find good limes you can add sugar or other sweeteners to your lime mixture. A new trend is to use "Agave Nectar" in Margaritas even in lieu of a liqueur. This sweet syrup, made from the agave looks similar to honey but mixes much easier and is becoming very popular with bartenders and chefs. Frozen Lime-aid works in a pinch and is often a better alternative to commercial sweet and sours.