I use color as my chief guide. But I always squeeze an avocado - you want the fruit to feel close to the skin. If you can feel a separation, the avocado is past its prime. The avocado should have a little give, but not much.
An artist fights to retain the integrity of a work so that it remains a strong, clear vision. Art is and should be the act of an individual willing to say something new, something not quite familiar.