In a mixing glass with cracked ice:
Juice of 1/2 lime
1/2 ounce Triple Sec
1 ounce tequila

Shake and strain into a chilled margarita or champange glass that has been edged with salt. (To edge with salt, rub the rim of the glass with a piece of lime, then dip and turn in a saucer of salt.

For St. Patrick's day, use green colored sugar for the rim of the glass, instead of salt..