A friend wants me to take one of her photos and make her skin "prettier". I know they do this in a lot of advertisements but not sure what the methods are. Anyone have a favorite way to make skin look smoother and younger?

Got this off another site
1. Use a good quality image which should be fairly high resolution.
2. Click SELECT > BY COLOUR
3. press SHIFT and hold it down on the keyboard while you click on all the skin tones in your image, make sure you click all the shadows, midtones and highlights on the face. Avoid the lips, eyes and eyebrows.
4. press CTRL C (to copy)
5. click LAYER > NEW LAYER
6. press CTRL V (to paste)
7. click the ANCHOR icon, in the Layers Palette.
8. click SELECT > NONE
9. in the layers palette click the eye icon to hide the bottom layer - now you will see something resembling a mask of the persons skin.
10. In the layers palette select the skin layer by clicking on it.
11. Use the eraser tool, set to a soft brush and erase everything that isn't part of the skin of the face. Also use the eraser around eye areas and everywhere there is detail around the nose and round the lips. Now you will have something that looks like a mask with holes where the eyes, nose, eyebrows and mouth are.
12. In the layers palette click on the LOCK check box, to lock the layer
13. Click FILTERS > BLUR > GAUSSIAN BLUR, change the blur radius to 10 or more until you get a nice smooth skin layer.
14. Click the eye icon to show the bottom layer once more.
15. Select the top skin layer again. Reduce the opacity of the skin layer, in the layers palette, by using slider until you get the effect you desire.

My favorite is to:

1) duplicate the layer
2) run GEGL bilinear filter (or Despeckle) on the duplicate layer
3) add a black layer mask to the duplicate layer
4) paint the layer mask white where I want to smooth things out.

Many ways to degrunge. I like to used ACE Grain Extract Overlay technique, but there is also inverse Highpass (the first method I've ever seen that addressed skin blemishes many years ago; I actually concocted the ACE Grain Extract Overlay method; lol). Take a look at the link below 2-Ton. Not sure if you will be able to see the images or not (sometimes you can; sometimes you can't if you are not a member; I am of course).

http://retouchpro.com/tutorials/?m=show&id=213

thanks guys, now I have a lot of playing to do!

If you have G'MIC installed you can also do the Select by Color which Rod described above and then open G'MIC and use Enhancements > Anisotropic Smoothing. Adjust the sliders to give the look you want. G'MIC actually provides several options for smoothing irregularities in tone or obscuring blotches.

I smooth skin usually just two ways, 1 is using the Anisotropic Smoothing filter in the GMIC plugin, and I also grab my fuzzy brush, and select my smudge tool, and I set the rate of it to 15, and I begin smudging on the parts I want to soften (of course you'd haft to adjust the brush size at some parts though too)

I bet some of the presets PC has created for G'MIC would work nicely for smoothing.

yes sure but as now i can't upload anything..
i suggest to try the Beauty Retouch filter from Tom Keil, now i am not sure if the last version is included in gmic, if not you may found a link in the gmic group on flickr

quite a cool filter and exactly for what you ask

ah, beauty retouch sounds easy...I like easy!

How do i get 'beauty retouch', i refreshed the scripts but it doesn't show up

I am not sure which version that came out on but there is a 1.5.0.1 and 1.5.0.2 that came out since your 1.5.0.0 version. Maybe it is in one of those.

ok i just installed 1.5.02 and found it under presets/testing

woo hoo glad it is working for you.

Fine you solved but that filter should not be there

Not your error or something to worry about simply that is not the logical place because that filter is already well tested so is not experimenthal for "testing "and IS a filter not a "preset".
So is possible would be moved at soon David will notice the incongruency in a more logical section (maybe "enhancement"?)

PS i suggest for question about gmic to start the topic title with "GMIC"..David browse often GC and is always interested in feedback on its app
I also didn't answered before because i believed your a generical question on retouch photo of nice girls not a speciphic question on a Gmic filter (that i know so i would have answered before ...but i overlook the topic because was not starting with GMIC )