Poke holes all over the hard avocados with a fork. This ensures the fruit will cook evenly and won't explode in the microwave.
Place the avocados on a paper plate. Arrange them in a circle on the outer edges of the plate; just as food doesn't warm evenly in the middle, neither will your avocados.
Adjust the microwave to medium heat and warm the avocados for 30 seconds.
Examine the avocados. They should be firm, but give slightly when you squeeze them. The skin should also turn dark brown as they ripen.
Return the avocados to the microwave if they aren't ripe enough. Heat them for 30 seconds at a time until they look and feel ripe. If the flesh still feels hard and doesn't give slighly when you press on it, pop it back into the heat.