When I start shading a piece sometimes I'll scan in the lineart and print out a few smaller copies to try stuff out like lighting, shading, negative and positive space all the neat artsy-fartsy junk that can make or break a shot. I'm no expert-blindly stabbing at the board until something starts to form that somewhat resembles the image I have in my head of what the finished piece should look like.
Mostly I fail.
Sometimes though I get lucky. This is some work for a commission that I was happy with on my first pass. That's usually not the case so score one for the hacks!