I'll give it my best try.
Once you have taken out mayor skin marks (Beauty marks, pimples, etc) with the patch tool (or what ever you use)
You create the Dodge and Burn Layer Set (D&B)
The dodge and burn is done with a set of curve adjustment layers.
From bottom to top:
Curve(LIGHTEN) lighten the mids and fill the layer with black to hide. In this layer, paint white at about 20% depending to lighten dark spots on the skin
Curve(DARKEN) darken the mids and fill with black as well so that you can use this to darken light spots on the skin.
HUE(DESAT) The HUE layer is used to desaturate the image and see better.
CURVE(CONTRAST) is helpful to display the dark/light spots better - an S curve in it to bring out the contrast so you can see it better
Both of them (Desat and Cont) can be turn on and off as you please.
After zooming 500% to work on the fine points of the skin, zoom out and use larger brushes to change light.
Then turn off the CONTRAST and HUE curves.
This takes a lot of time, but the result is the best I could achieve.
Hope this helps...
More... Sometimes, I duplicate the set in case some dark spots are really dark and just one lighten won't do it.
More2: English is not my native lenguaje... so sorry in advance