Czechman's technique for creating smooth, natural skin in Photoshop, just one tip from his book:

SKIN
TWELVE SIMPLE STEPS TO PROFESSIONAL PORTRAIT EDITING
© 2009 Woody Vondracek

DISCLAIMER: There are numerous ways to accomplish things in Photoshop, almost as many as there are photographers.
This is how I do it because it's simple, it's what I was taught, and it works for me.

STEP 1

 No one has perfect skin and although Amanda is a very pretty young woman, there are issues here that need to be addressed if we want a professional portrait.

STEP 2

Before you do anything, use the Clone tool, Healing brush, Dodge/Burn tool and Paintbrush to remove blemishes, clear bloodshot eyes and whiten teeth.

No matter what you do next, you will be wasting your time if you don't get this part down to a science.

At this point you should adjust the Levels ONLY. Do not do any sharpening yet.

Detailed instructions for removing blemishes and correcting levels are found in the book.

STEP 3

Next, select the entire face and any other skin with the Lasso or Magnetic Lasso tool set to 1 pixel feather.

Then create a new layer from the selection: Cmd-J (Ctrl-J on a PC)

With the new layer selected, choose Filter / Blur / Gaussian Blur and set the radius to 30 pixels for any capture 6 to 12 megapixels. This is not critical to the final product - just try to match about what you see here.

This is what you will see after applying the Gaussian Blur.

STEP 4

Next, select the Eraser tool set to 50% Opacity / Airbrush mode and make the diameter of the brush large enough to cover the entire frame.

Make one pass over the entire image and you will wind up with this.

STEP 5

Next reduce the diameter of the Eraser to about the size of the eye and erase over any hair including eyebrows and the upper and lower eyelids.

You should have something like this now.

STEP 6

Next set the Eraser tool to 100% opacity and erase over the eyes, lips and teeth. Clean up around the hair, fingernails, clothing and jewelry if they are in the photo you are working on.

To be sure you have gotten everything, hide the background layer and check for missed spots.

You should have something like this now.

STEP 7

Next sharpen the bottom layer by using Unsharp Mask. Pay close attention to the the way the hair and eyes react to sharpening. You want them as sharp as possible without getting halo artifacts

Detailed instructions for using Unsharp Mask are found in the book.

Now select the top layer and adjust the opacity until you have a natural skin texture. The object of all this is to make your subject look like they have perfect skin, not like they've had a face air brushed onto their head.

You may also want to go into Levels or Brightness/Contrast again just to be sure your colors are pure.