Use 100% agave tequila labeled white, silver or blanco. I recommend Milagro, Hornitos or Espolón.
Salted rim considerations:
Consider lining the rim of just half your glass with salt so you can control how much salt you taste with each sip (that’s a great tip I picked up from a recent issue of Bon Appetit). If you’d prefer a light sprinkling of salt all around the rim, just pour a very thin layer of salt onto your plate and run the lime slice around the entire rim of the margarita glass.
I've found that the easiest way to juice limes is with this hand-held juicer
(the yellow one). Citrus at room temperature is easier to juice than cold citrus, so take your limes and oranges out of the fridge an hour in advance. Here's another tip, from Brenda, a reader: Before you slice the citrus, roll it back and forth on cutting board, pressing slightly. Then cut it in half lengthwise, not across! You will get up to 1/3 more juice that way.
Want to make a pitcher of margarita?
For 10 drinks (about 45 ounces, or 5 1/2 cups), combine 2 1/2 cups silver tequila, generous 1 3/4 cup fresh lime juice (around 15 limes), 1 1/4 cup fresh orange juice (about 5 medium oranges) and 3 tablespoons plus 1 teaspoon light agave nectar. Mix well, and add ice. Don't forget to garnish your rims with lime rounds and coarse salt.