Put your whole avocados in a paper bag and set them on the counter. As the avocados ripen, they produce ethylene gas, which will concentrate in the bag and ripen them faster.  If you want your avocados to ripen even quicker, place an apple and/or a banana in the bag as well. Concentrated ethylene gas from multiple fruits speeds up the ripening process even more. The avocados should be ready to use in 1-2 days. You will get similar results by putting an avocado in a bowl and covering it with dry rice.