I love making smoothies with my avocados so I prefer mine to be pretty ripe when needed, and will usually make at least 2 smoothies per week. With 2 avos per smoothie that's at least 4 avos that I'll buy each weekend at the supermarket.

Depending on the available range when I get there, I try and grab a couple that are darkening on the outside already and have just a faint hint of give in them when gently squeezed, and another couple that aren't quite so ripe for later that week. I'll sit them all out on a plate on the coffee table in the living room and just let them ripen of their own accord, with the added option of just placing any in the fridge that I feel might be getting a little ahead of themselves, just to slow the process down a little.

There's a bit of trial and error to it I suppose, but you start to get the hang of works best for you with a few goes. It's not like avos are too expensive anyway (at least not for me where they're in season right now).