Well, I have a list of questions I ask myself toward the end of a painting. When I feel that I have successfully answered those questions, I am done. Are my shapes believable? Are my shapes and values visually linked (are my darks visually linked)? Are my darks and color balanced? Do I need more contrast or "volume" in any areas? Does my painting and direction or movement in the painting "read" like I intended? How does the viewer's eye move around the painting? And finally, are there any small details I could add or remove that will enhance the flow or design in the painting?