The Unsharp Mask is the tool most often used to sharpen an image that is a little softer than the retoucher wants.  The Unsharp Mask dialog has three adjustable sliders: Amount, Radius, and Threshold.  (We won't discuss Threshold here.)

Most books recommend an Amount of 100-200% or greater, and a Radius in the vicinity of 1-2.  The result can be seen in the upper right image, and is quite typical.

There is a little-known variant of the Unsharp Mask, however, which uses an Amount of ~20% and a large radius, ~100 px.  The effect of these settings is to produce more of a change in contrast than a change in sharpness.  (I typically reduce the effect using the Edit/Fade tool at 50%, as seen on the lower left image.)

The final image (lower right) shows the result of combining these two variations of the Unsharp Mask.  (I use them individually so much that I have made actions for each.)