Cut the avocado, remove flesh: Cut the avocados in half. Remove the pit. Score the inside of the avocado with a blunt knife and scoop out the flesh with a spoon. Place in a bowl.
Mash with a fork: Using a fork, roughly mash the avocado.
Add salt, lime juice, and the rest: Sprinkle with salt and lime (or lemon) juice.
Add the chopped onion, cilantro, black pepper, and chiles. Chili peppers vary individually in their hotness. So, start with a half of one chili pepper and add to the guacamole to your desired degree of hotness.
Serve immediately, or if making a few hours ahead, place plastic wrap on the surface of the guacamole and press down to cover it and to prevent air reaching it.