Did a demo for one of my friends, looking to paint in Photoshop with a mouse. I used a Rick Berry painting and tried to emulate it some by using Warp, Liquefy, the Smudge Tool (sparingly!) and mostly harsh lines. I learned in the process myself!
In closing, if I were teaching a class on digital painting, I would require the first project to be done with a mouse. I like how intentional one must be under that restriction.