Pour thawed limeade into a suitably sized container. (Because I make it as a batch to store, I save a juice bottle for this.) Not all stores carry frozen limeade in the wintertime, so I have occasionally used frozen pink lemonade.
Using the empty limeade can to measure, add equal amounts of tequila and triple sec.
When you are ready to serve, pour over ice. Or make a nice slushy frozen margarita by mixing in a blender with ice. Salting the rim of your glass is optional. Sometimes I add fruit or juice -- mango nectar, pineapple, strawberries (!). With or without the addition of fruit, topping this off with just a little added tequila gives your margarita a nice kick.
Enjoy! (And drink responsibly, don't overindulge because it tastes so good.)