This is our original image - a professional page 3 model shot by a professional photographer (heavily cropped for any minors reading) but she's not exactly a pinup right now. We're going to change all that :)

1. The first thing to do is clone out the few stray hairs over her left (right on the picture) eyebrow. Take skin samples close to the cloning area to remove them then finding a clear patch of forehead to sample from use a large, soft healing brush to smooth the texture of the area.

2. Now that we have a fairly clean palette to work on we can start painting.
Create a new layer then select a fairly large, soft brush with a very low opacity (5-10%).
Analyse the areas that need the most improvement - the chin, mouth crease, nose shine and eye bags. Look at the section you want to paint and find what you feel is the average colour of the 'correct' skin patch and take a sample. Brush lightly over the areas until the unwanted feature is removed.
Then do the same with the rest of the skin to smooth the texture and tone.

3. She's should be looking a little flat and matte right now but thats about to change, first we need to match the grain of the image. If the image if very high res this may not be necessary but it cant hurt ;)
Go to filter -> noise -> add noise and add a little noise usually between 1.5 - 3%. The exact settings will depend on the resolution and quality of the image you're working with. Make sure you have some of the original image showing the the preview window and zoom in close. Try to match the natural grain of the image as closely as possible.

4. Now we need to bring a little bit more of the girl out from under the makeover. Take the layer opacity down until you can see a little of the shine of her skin, the hint of freckles or pores - basically we want to see texture but not the uneven skintone or the blemishes we were painting out. You want the overall look to have good texture, dont worry if there are a few bits of wrinkle or blemishes showing through, you can repaint small areas to build up the colour a little where needed.

For just a simple retouch I would stop here, we've smoothed her skintone, removed unsightly parts and left a fresh, naturally looking picture. But we want to go drop dead sexy. We want to emphasise the pout and the 'bedroom eyes'.

5. At this point we want a fresh copy of the image to work with - so create a new layer and holding down alt go to layers -> merge visible. This creates a new layer with our retouched girl as a base for our image.

6. Duplicate the layer and set the blending mode to overlay, you should already see the improved colour contrast and warmth. You may also notice that little bit of texture and 'realism' we left in her skin is also emphasised. We can fix this by applying a gaussian blur and a noise -> median filter. For this I used a gaussian of about 5 and a median of 15 but play around till the skin looks smooth.
We've also lost the eyes, they've become very dark, we need to bring them back. Add a mask to the overlay and black out the eyes to see the layer beneath, this should emphasise the eyes and make them very engaging.
You may also want to add a layer on the eyes to enhance the colour. Create a duplicate of the retouched base layer and use the curves adjustment to enchance whatever colour eyes your subject has, then hold down alt as you press the layer mask button, this will create a black mask and you can paint in the enhanced eyes at an opacity to suit you.

Right now she's looking pretty good but her lips could do with a little gloss.

7 . Create a new layer and fill it with 50% grey. Set the blending mode to softlight then with a low opacity soft white brush start painting on some highlights paying close attention to the highlights already in the picture. We want to strengthen and enhance them, not change them. You may also like to add a little gloss to the iris to give her eyes a brighter look.

The full image, along with other retouching/manipulation jobs can be found here: http://www.hazelryan.co.uk/Inspiras/gallery.php?bigfile=DSCF0286a2.jpg

Warning: The above link contains female nudity, although the image is very tastefully shot and is no worse than appears on page 3 of certain newspapers (no nipples or genitals are showing) it may offend some or be unsuitable for children.

I hope you enjoyed this tutorial and found it interesting and informative.