To have light in the watercolor, you have to paint around it to preserve it. There's something what I liked to call the "breathing room". The paintings will feel dead when you try to fill everything in, because you didn't leave any breathing room. 

  To differentiate one artist from another, master to apprentice, is their sense of shape. If you strip away everything else, technique, ability to mix color and put down washes, shape is the defining element that makes a master who they are.