Here is a another quick and very useful photoshop tip for retouching a skin.
1. First open the picture of-course. I will use this picture for example .
2. Duplicate the layer (CTRL+J)
3. Median filter on the duplicated layer (Filter -> Noise -> Median). In my picture i use 3 pix radius (my picture is 10Mpix).
4. Set the duplicated layer as Lighten from blending options in layer palette.
5. Create a layer mask (still on duplicated layer) and fill the mask black.
6. Now with white color soft brush treat the skin carefully.
You will see how soft and shiny become the skin and the skin texture remains almost the same.