Cut the avocado in half, scoop out the flesh with a spoon; mash 3/4 of it well and chop the remaining 1/4 coarsely (I do this with the spoon, in the avocado shell, before scooping the last bit out).
Mix it into the mashed portion.
Mix all remaining ingredients together
Serve immediately, or cover with plastic wrap, pressing wrap firmly to surface of guacamole (or it will turn color due to oxidation) and refrigerate up to 4 hours before serving.
(Just a tip I saw on T.V., to be sure that you get a nice green avacado, peek under that little stem.. if it's bright green, the avacado is good.. if its black, then the avacado will have black spots inside.)