Start with ripe, not-too-soft avocados. Remove skin and pits from avocados and place in medium-sized bowl. Reserve a pit or two for later – it is said that leaving the pit in the guacamole will preserve freshness and keep the mash from oxidizing and going brown.
Add garlic and juice of half of lime to avocado (or whole lime if you are using 4 avocados). Mash well.
Serve immediately, or place reserved pit(s) in bowl an refrigerate, covered (plastic wrap touching the surface of the guacamole), and use within 24 hours.
see more thorough instructions at http://craftyfork.com/2012/01/15/guacamole/