I'm working on a picture book proposal. I decided to borrow Alex Ross's technique. I first painted the scene with black gouache on 12" X 12" cold press watercolor paper.
Next, I started laying in color with Van Gogh watercolor paint. The overall effect isn't too bad, especially considering I haven't picked up my paints in at least a couple of years. Not surprisingly, smoke is difficult to paint and took up most of my painting time.
It helps to have a great model as well (my son).The superhero uniform is thermals, Spider-man gloves, Mama's snow boots and masking taping.
I couldn't decide where to paint, so I bought a 2X2 sheet of 1/4" plywood, sanded it, and used it as a mobile art desk. Worked great, as I could move the board around while painting instead of contorting into uncomfortable positions like I used to. This probably took around 6 hours.