Perfect Margaritas

I can't believe I'd ever forget this recipe, but am posting it here in case I do. 

The key thing to remember is 2 to 1 to 1: two parts tequila, one part liquor, one part fruit juice. Serve on lots of ice, and in a rim-salted glass if possible.

The best version so far:

2 shots of Partida 

1 shot of Cointreau

1 shot of fresh-squeezed lemon and lime juice (this should be about 2/3rds lime, 1/3rd lemon)

Drink -- preferably along side some homemade guac and chips -- and don't plan on driving anywhere anytime soon.