To make an easy guacamole dip, mash 2 peeled and diced avocados with a fork. Add 1/4 cup of cilantro, 1 chopped serrano chile, the juice of 1 lime and 1/2 a chopped white onion. Season the mixture with salt before serving it.
The trick to great guacamole is to use ripe avocados. When you press them they should have a little flexibility. If they don't, they aren't ripe yet. Be careful they aren't too soft, which indicates they're overripe. In any case, a taste test is the best way to confirm quality.
To cut the avocado, hold the avocado firmly with one hand and with your other hand use a knife to slice it lengthwise along the perimeter. Open the two halves to reveal the seed. Take the side containing the seed and make another lengthwise cut to remove it or take a spoon and scoop it out. Once the pit is out you can either scoop the fruit flesh out of the rind or take a knife and make cross-hatch incisions, careful not to cut the peel. Then scoop out the pieces gently with a spoon. It's normal for there to be some areas of brown on the avocado flesh, and with guacamole, it won't be noticeable once everything is mashed and mixed.
For a slightly more complex variation, toss 3 peeled and seeded avocados in the juice of 1 lime, then drain them. Save the lime juice. Mash 1/2 teaspoon each of salt, cumin, and cayenne into the avocados with a potato masher. Dice half an onion and 2 Roma tomatoes. Remove the seeds from 1 jalapeno pepper and mince it. Add these vegetables to the avocado mixture, along with 1 tablespoon of cilantro and 1 minced clove of garlic. Mix in 1 tablespoon of the reserved lime juice. Allow the guacamole to sit out for one hour to let the flavors mingle.
To make a creamier dip in only ten minutes, peel and seed 4 avocados and place them in a food processor. Add 1 cup of cilantro, 1/2 cup of sour cream, 1/4 cup of lime juice and 1 jalapeno pepper. Season the mixture with salt and pepper, and blend it until it reaches a smooth consistency.