It's all a matter of taste and practice seems to make it better each time.. Simplicity is key though- all these recipes steer in the right direction.
3 *ripe* avocados http://en.wikipedia.org/wiki/Hass_avocado
2 chopped medium tomatoes
1 finely diced white onion
½ cup of finely chopped cilantro
1 splash lime juice
2 x small green chilli finely chopped
Salt to taste - add just a little to start..

Is what I personally go by