1. The most important thing is to begin with a good, well-exposed photograph. This isn't a way to fix a bad image, but a way to make an already good image even better. This is an image I got off stock.xchng (http://www.sxc.hu) by Guy Scholiers, but any well-exposed image will work.
2. How can you tell if an image is well-exposed? Aside from the obvious (look at it), check its histogram. Make sure there are a good amount of values all the way from left to right, with no gaps at all (none, this is very important). Ideally, the histogram will taper off at both ends, precisely reaching zero at both the far left and right corners of the histogram. Here the shadow (left) side tapers to zero, but the highlight (right) side is clipped. Luckily, for this image the shadows are more important.
3. Run Image > Adjustments > Equalize. This redistributes the brightness values so they are evenly distributed. Notice in the histogram that this is destructive, so work on a copy. The holes in the histogram also illustrate why it is important to start with a good image (working with 16-bit images will lessen the number of holes).
3. Duplicate the background layer, run Image > Adjustments > Desaturate, and set its blending mode to Multiply. This will make the image considerably darker.
4. Add a layer mask to the multiplied layer, and with a large, very soft black brush set to a low opacity, slowly paint in the subject area to highlight it.
5. Add a new blank layer to the top of the stack and set its blend mode to Overlay. With a large, very soft black brush set to a low opacity paint around the edges of the image. Paint so that it gets progressively darker towards the edges. Make sure there are no gaps on any edge. This is called "edge burning" and focuses the viewer's attention on the subject.