Create light and shadow
To create a light (or shadow) effect across a broad area, I use a Layer and Levels technique. I duplicate the subject layer, lighten it using Levels, then add a Hideall mask. Then I paint on the mask to reveal the lightened layer, which gives me control over the effect of the light. By Levels-adjusting a duplicated layer I control what happens to the details and texture, unlike when simply painting to lighten or darken something. Then I can focus on the light effect and not worry about losing details.