Tom's book Watercolor Painting is one of the best books I have found on the subject. The book is not about here is how you paint a tree, or a landscape or a street. Instead, the book is about taking any scene, deconstructing it to make sense of it, then putting it back together into an effective painting. It is not a book you flip through the day you buy it, be inspired for the day or the week and never look at again. It is a book you will go back to over and over again for months (or maybe years! I don't know because it hasn't been that long for me yet :) ), and still not scratch the surface.
Everytime I go back to his book I realize that I am able to go a little farther in it, and I take it as a measure of my growth. Yesterday I read the chapter on Seeing in Layers, and today's exercise is motivated by that.
For the exercise I chose a picture I took in our neighborhood with a simple subject and good shadows.
I did a quick value sketch to get clarity on the big shapes and their relative values.
Next I did two studies as shown below. On the left there is the monochrome value study, based on the value scale I have identified above. On the right I did a geometric color study where the shapes are simple, and done with two layers and mostly local color and shadow color.
The next thing I did is a 'Seeing in Layers' exercise, where the picture is broken down into multiple shapes, and we go from painting the large shapes and going towards the more specific.
If you don't have Tom's book, do yourself a favor and GET IT!!