I finally feel like I've gotten the hang of using the airbrush tool. By doing additional brushwork on upper layers, tweaking them, then merging down onto the main image it gives me much more control over the placement of my values. I'm finally understanding how all these artists were able to get such great skintone transitions... Anyways, the above image is a test of this new technique. No photo references used either. :)
One of my friends told me that I should airbrush cars. I'm starting to consider the idea more and more seriously.