Thinks to know:
-I used three kinds of brushes. A chalky one, plain airbrush, and a smeary one (oil like). And "dodge tool" in airbrush mode sometimes. I recommend Screen and Softlight option for your painting tools in some cases.
-In my layers I made a selection of the silhouette, then painted it flat, clicked the "preserve transparency" option and I forget about the whole thing of painting outside the figure.
-During the first coloring steps I used three layers. First one: the pencil drawing (opaque & below all). Second: a yellow multiply layer for a yellow base and Third: another multiply layer for the main shadows. All volume of the third step was done freehand with different grays and brushes, changing transparency of my brush very very often.
-I FREE-PAINT THROUGH ALL THE PROCESS, in between my color adjustments.
-I'm addicted to color adjustment tools. Color balance, hue-saturation, curves and even Variations (see the red coat in the 5th step, for example). And Levels to keep contrasts alive all the time.
-In the last step, I flattened the whole thing to paint more highlights without layers and clean some pencil dirt. I love that part.
-I don't have a steady method, so It's difficult to keep track of my "tricks". HONEST! I just use anything that PS offers me... Pay attention to the pictures and figure things out. It's the best way to learn.
Hope this helps, folks...