Every artist needs to learn to do a self critique - to look at his or her painting and be able to see what your painting may need to improve or finish it.
This information comes from Kathleen Dunphy's blog. Kathleen is a wonderful west coast oil painter who also paints the Maine coast. I had the privilege of seeing her work when the Plein Air Painters of America exhibited at the Cape Cod Museum of Art a couple summers ago.
Kathleen Dunphy keeps a "Critique Notebook". She records the date, size and location of her painting.