I always do this activity before the first Art project of the year. We make a list of what Art IS, and what Art ISN'T. This really helps them set their own expectations of what finished art projects should look like, and that it really does take time and should be neat, but doesn't have to be perfect. We bring these points up periodically so they can evaluate how they are working. I don't grade them on the perfection of the art, but their willingness to try new things!