Helo friends.... i find the rough skin chaning into smooth skin... lets look at this....

step 1:
my golden rule is duplicate the layer... now just hide the original layer and the fun begins now... here i take this beauty picture it is a little dull

step2:

Erase every thing except the skin.... and may use the eraser tool at different opacities at different places.... here i did like this...

step3:

Now after erasing , simply ctrl click on the duplicate layer ... now the image is selected....like this.

step4:

Now go to filter --- blur -- gaussian blur and give the measure as u like ...... i give the radius like this

step5:

The final step is just adjust the opacity as u like .... here is the final image ... thank u very much

I hope u enjoy this very much...... :)