Juice one lime. Lemon is okay if that is all you have. Juice from the little plastic lemon or lime is NOT okay.
Open two small avocados or one large one. They need to be ripe! Your best bet is to buy them a few days ahead of time and then make guacamole once the fruit yield to a gentle squeeze.
Mash the avocados into the bowl containing lime juice. The reason you do it in this order is that the avocado flesh turns brown very quickly when exposed to the oxygen in air. The citrus juice prevents this.
Add around 1/4 cup of finely minced red or yellow onion and a similar amount of chopped fresh tomato.
Add a jalapeño or other hot pepper--finely chopped or a few shakes of Tabasco Sauce is good too.
Complete with garlic powder, cumin, salt and black pepper. You may also wish to add a couple table spoons of sour cream. Minced crispy bacon is also a nice touch.