TIP: To ripen avocados, place them in a plain brown paper bag and store at room temperature. It will take about two to five days until they're ready to eat. To hasten ripening, place an apple in the paper bag with them.
To store a cut avocado, the California Avocado Commission recommends you "sprinkle it with lemon or lime juice or white vinegar and place it in an air-tight covered container in your refrigerator. Eat within a day or two."
"If refrigerated guacamole turns brown during storage," the Commission recommends discarding the top, browned layer.