Before you begin, make sure the avocado is ready. It needs to be very soft to the touch (but not bruised), and the skin should be very dark in color. Slice open the avocado and place in a small mixing bowl. Set aside the seed.
Add the lemon juice over the avocado (lemon juice adds flavor and slows browning).
Mince the jalapeno and add to the bowl. Note that you can seed the pepper to reduce spice--or for more spice, use an orange habanero instead.
Mince the cilantro and dice the onion. Add to the bowl.
Stir these ingredients with a fork, mashing the avocado evenly.
Add the garlic salt and cumin (for a richer spice flavor, use more cumin).
Mix the spices in and set aside (rumor has it that adding the avocado seed into the guacamole will sustain freshness and further reduce browning) or serve right away.