Remove pit (hold the half of avocado with the pit in one hand, firmly but gently smack a chef's knife into the pit until the knife sinks about half inch into the middle of the pit, twist the knife and the pit back and forth to loosen the pit and remove).
Score the flesh of the avocado with the tip of the knife.
Scoope out the flesh with a spoon into a small bowl.
Mash the avocado with a fork, leaving some chunks.
Fold in tomato, onion, lime juice and salt.
At this point, I usually watch my husband inhale the guac with some authentic chips from the local Mexican market.
Note: If you are going to put the guac into the refrigerator, save the pit and put it in with the guac to help preserve the avocado.