When I do any dodging or buring on an image, I use the following method to accomplish the task
- Create a new layer, fill it with 50% gray, and set the blend mode (in the layers palette) to overlay (in the overlay mode the image is visible - the 50% gray does not impact the image). Dodging/Burning this layer will lighten or darken the gray level and thereby lighten/darken the image in the areas you want
- working with either the dodge or burn tool, I set the tool to shadows, mid-tones, or highlights and then i set the exposure to something in the 15-20% range
- I usually work with a soft edge brush. I brush over the areas I want the dodge/burn effect - with the low exposure setting the effect on the image is very subtle
- I will make a copy of the layer that I just did the dodge burn on - this basically doubles the effect. I continue to duplicate the layer until I get the desired amount of dodge/burn. Don't worry if adding a layer makes the effect too much - see next steps
- Merge all the dodge/burn layers you just created and make sure the blending mode is still set to overlay
- If the effect is too much, then I use the Opacity slider to dial back the effect
- I'll also sometimes do a light Gaussian blur on the dodge/burn layer to smooth out the edges
