A helpful tip when shading and ligting - add a new layer, go to Edit, then Fill, fill the layer with 50% Grey and then change the Blend mode to Overlay or Soft Light, then with a low opacity (10-15) use the brush tool with black where you want the shadows, and white where you want the light
This way you can dodge and burn without changing the coloring, which dodge and burn tools often do. Hope this helps you out