Thanks for the advice Yo and everyone else who responded to my post below. Here are some renderings I’ve been working on. I basically use this technique: (bottom layer to top in that order)
Bottom layer: Background-white with a “marker wash” created using wacom tablet.
Color Layer: Use paths to create basic colors of objects. No shading here.
Shadow Layer: (set to Darken) I use a large airbrush with black ink set to about 15% opacity and build up the shadows.
Highlights Layer: (set to lighten) Same as above using white ink.
Scanned Sketch Layer: (Set to Multiply) Black prismacolor on vellum for that smooth look.
Top Highlight Layer: Here I put farkles and LED glows that really make the drawing pop.
I also create and save numerous paths that can be converted to selections quickly.
Here are some examples:
I have a few more non-photoshop sketches on my website if you are interested in taking a look at http://www.concept-engine.com/sketchbook.html
What do you think?