1) Buy them before you need them.
2) Make sure they are too hard to use
3) Put them in a paper bag in a warm spot. If you're in a big hurry, cut an onion or apple and put it in the bag.
4) Check them periodically until they are just soft enough (you'll know)
5) After ripe, store them in the fridge until you use them. We both know you'll use them soon.
Beware the Florida avocado, aka the Dominican avocado. They are less fatty and more watery, are a bit larger, and have a smooth, lighter green skin. No comparison to the Hass avocado, imho. We can't grow the Hass down here, cause diseases take them out. Too hot/humid.