If I’m painting daylight, then the shadows need to look great. One way to do this is to start lighting the characters with the ambient light in the scene: the warm light bouncing off the ground, the cool light from the sky and the soft rim light from the explosion. This can be as detailed as I want.
Key light sculpting
The ambient light underneath enables me to paint the sunlit areas on a separate layer and then erase it where I need shadow. This part of the painting is like sculpting: I’m pushing and pulling the light until the forms have the roundness they need. My goal is to put the highest contrasts where I want people to look, such as faces.