Slice each avocado lengthwise around the pit, twist to separate the halves, then tap the pit with your knife blade and twist to remove. Scoop the flesh into a wide mixing bowl using a spoon — wide bowls make mashing much easier.
Pour the lime juice and sprinkle the salt directly over the avocado. Using a fork, mash the mixture with deliberate strokes, leaving plenty of chunky pieces — you're not making baby food here. Stop when you have a mix of creamy and textured avocado.
Gently fold in the diced onion, minced jalapeño, chopped cilantro, and garlic if you're using it. Use a spoon and fold rather than stir — aggressive mixing will turn your chunky guacamole into green mush.
Take a small taste and adjust the balance — more lime juice for brightness, more salt for depth. Remember that flavors will meld as it sits, so don't go overboard with adjustments on the first taste.
Serve right away for the brightest flavor, or cover tightly with plastic wrap pressed flush against the surface to prevent browning. It'll keep in the fridge for up to 2 days, though it's always best within the first few hours.