Put juice in the blender. (You may want to add a few tablespoons of superfine sugar if you like your margaritas not as dry, or as much as a 1/8 of cup per person if you really like 'em on the sweet side. In the frozen version I like them just off-dry, thanks for asking.)
One ounce of Cointreau, one jigger of plain ol' white/blanco/silver Cuervo tequila per person (Seriously, any tequila more posh than this would be wasted, as the subtle nuances would get lost amid all that ice and coldness.)
Shave the ice. (If you are planning to shave a LOT of ice, you may want to do so into a colander over a bowl, to prevent any undue dilution.)
Put all in the blender. Blend (2 second pulse-another 2 second pulse-run at max. speed for 10 seconds-2 second pulse-2 second pulse).
After blending take out a margarita glass from the freezer.
Serve. You are now in good shape to brave the TV news, newspapers, and other aggravations.
Repeat as needed.