I decided to start with robots. First up - a Warbot!
I start with a pencil drawing, then ink in photoshop using stroke paths. I actually use two different brushes on the same path: a standard size 20 line and then a size 40 brush line to add line weight.
Then I take a page from Drawing with Jazza for shading. I use a layer set to multiply and color in grey tones where I want shadows.
Lastly, I through a color layer under everything. The nice thing about throwing the color under the shading is that it is easier to swap out the colors.