The above watercolor is very simple, yet I like it. Why?
The main reason I think this design works is that there is a clear dominance of shape, size, color, and value. There is no question but that the boat shapes are the main actors in this piece and the largest one is the star. Warm hues are also clearly dominant. Finally, values are mainly dark to mid-tone, allowing for strong contrast with the white center of interest.
Sometimes when I start a painting, I just start brushing in colors. But instead, if first I take a few minutes and plan a dominant shape, color, and value, I think the result is better.