Duplicate the background layer.
Menu: Layer -> New -> Layer from background.
or
In the Layer palette, drag the background layer down to the new layer
icon.
In the new background layer apply a gaussian blur
to it for smoother skin, setting the radius in the range of 2- 10.
Menu: Filter -> Blur -> Gaussian blur
Add a black layer mask to the blur layer.
In the layer palette, click on the layer mask button (black square with
white circle in the middle).
Fill the layer mask black
Menu: Edit -> Fill -> black
Select the brush tool and brush the areas you want to smoothen.
Select an opacity in the range of 20-50%, select the appropriate
diameter, select a soft edge.