I move avocados into the refrigerator at the first sign the skin yields to slight pressure.
When I only use half an avocado I leave the seed in the half to be stored, squeeze a lime wedge over the exposed flesh, cover with cling-wrap and refrigerate.
This is pretty much the only time they go on sale, so we buy them. I let them get ripe on the counter. As they ripen I take out the flesh, mash or chop it, put it in 4-8 oz canning jars, put lids on, and freeze to use during the year. It stays green and they can be thawed overnight on the counter, or at a low energy setting in the microwave. I have 6 on the counter right now ripening.