I've been working on some new paintings lately. I want them to be the best that I can make them (with the skills I currently have), and at the same time they need to be done. I could paint, and repaint areas to make a piece THE BEST PICTURE EVER, but I don't think that's very realistic.
So how do I know when a piece is done? I think for me it's probably a combination of criteria, and practicing distancing myself at times from the piece. To become the observer rather than the maker. Sometimes this can be tricky.
How do I feel about the picture? or How does it make me feel? If the answer is something like "frustrated" or "it doesn't feel like it has that 'magic' yet", maybe it's time to switch to a different track of questions. I've been coming up with alternate questions to ask myself to gauge if I think something is done.
Do I like how it feels?
Does it have the mood I wanted? If not what mood does it have?
Does it have an interesting look?
Does it have a pleasant look?
Does it feel complete? If no, does it LOOK complete? If no, what's missing or tripping up the visual?
Is everything worked to the level of finish suited to their position in the visual narrative? (For me this includes use of composition, value design, color temperature, and edges).
Does something need to be played up or down, enhanced or subdued?
Are the values unified or are they isolated? This is usually a feeling for me, that it feels "splatty" if it's not unified.
Is the center of interest or theme really coming across? Can I say, "Yes this picture is about this thing"?
Because sometimes done is better than trying to make it perfect. That's not to say that I won't keep trying to make each new picture the best it can be. Sometimes it's good enough. I did what I could with it, or I learned some things from it and now it's time to try another.