STEP 1:First, take a sample image as your choice.

STEP 2:Next, grab the smudge brush. Pick a non-hard brush (can be 0% hardness as well), set the strength to 5% and start smudging. Cover every part of her face except the eyes and teeth.

STEP 3:Next, duplicate the layer and use the following settings:Blending Mode: Screen, Opacity: 45%.
Then duplicate the layer again, and use the options in the screenshot below.
STEP 4:If you want to add a small shiny/glow effect to the skin, you can pick up the dodge tool and using the settings in the screenshot below, you can start dodging areas you'd like to be brighter.
Now compare the two photos
it is a very simple technique of using smudge tool in photo retouching