1. Sketch on a new layer at 100 dpi
2. Make background layer grey then lightly add basic color to that layer. Paint lightly
3. I make a third layer and fill it with a warm color (or cool color if you like.) Bring the opacity down to about 50%
4. Make a fourth layer and start lose painting. Don't zoom in to much. Make sure you're paying attention to value as well as color. ( You can check your value by adding a color layer over everything and filling it with black.
5. Flatten entire image. Uprez to 300 dpi. Begin tightening the painting and details. When you're done with details is entirely up to you.