link). In one chapter, Carol suggests setting up small study subjects and painting for 20 minutes: reposing the object (or simply restarting) and repainting the same thing.
Here is such an exercise. These are the last of my nasturtiums as cold weather finally arrived and finished the 2014 tender plants. I divided an 8 x 10 board using 1/4" artist tape. I painted each square for about 30 min (I went over the alarm). When all were finished, I decided to paint in the white borders and extend the bright leaves over the edges to attempt a composition of the exercise. This was fun. I did improve (can you find the first and last small painting?)
So far, this book is excellent. Perhaps you want it on your Christmas list.