If you wanna go all out like the glossy mags do, first use the stamp tool to smooth out the obvious blemishes, then copy the layer. (Drag it onto the “Create new layer” button in the layers window.)
Hide the top layer, and then use the gaussian blur filter on the bottom layer until the skin looks very smooth and no pores are visible.
Show the top layer again, and use the Sharpen filter on it.
Set the opacity to about 30%
Add a layer mask on the top layer. (The button is in the layers window.)
Working on the layer mask, use the airbrush (set the colour to black) to trace all the spots that should be detailed. (Hair, eyes, edges of nostrils, etc.)
Adjust the opacity of the top layer until it looks right.
Congratulations, you’ve got no pores, just like Brittney Spears. (Or at least her photos.) You may like this effect, or you may find it creepy as hell. COSMO readers can’t get enough of it, it seems.
This is also a good way to get rid of surface wrinkles on old prints. (The before/after .gif doesn’t show nearly as much detail, particularly the aging, as the print-quality image-- but you get the idea.)