A friend just showed me a pen-and-ink drawing he made of a Taos Pueblo. It was really impressive. (I'm not an art critic but I thought it was terrific.)
Somehow we got started talking about perspective. In his art class, he said, his teacher tells them to stop working after an hour or two and step away from their work. They should walk across the room and study it from different distances and angles.
I think that translates to our writing, too. Give it some time and distance, look at it from a different perspective, be objective. Be honest. Critique yourself constructively and build on what's good.
Writers paint pictures with their words, not brushes, but our goal is the same: to make something beautiful.