In no way I am to be considered a professional photographer, but this method of sharpening images comes straight from them. It's an easy tip, that might come in handy, when you need to bring that extra something to your image. Oversharpened images can be awful to watch, so please be careful, not to overdo it.
Here is an example of an image, sharpened this way:
click on the screenshots to get a bigger view
Open your image
Add the filter
Select Filers > Sharpen > Unsharp Mask...
Apply the filter
Now this is the part where this filter differs from a usual sharpening filter. You have 3 sliders that you can adjust. The Radius and Threshold should be kept low; 0.5 - 1 works just fine. The Amount slider can be adjusted to your liking. For example for this image a 100 worked. For some that turned out sharper in camera a 80 will suffice, where sometimes, images that come out soft need a 120.
Amount. The Amount slider is used to control the amount of contrast between differing pixels, which affects edge contrast. Higher values equal more contrast and lower values equal less contrast.
Radius. The Radius slider is used to determine the number of pixels that are changed when the filter sees tonal variation. Higher values increase the size of the halos, causing the sharpening to be obvious. Be careful because of this, since high values can cause oversharpening. Keep in mind that this value is going to vary depending on the subject matter. A lower value works best with photos rich in edge detail, while a higher value can be used for photos that don’t have as much detail in them.
Threshold. The Threshold slider is used to determine how different in tone the surrounding pixels need to be before they’re considered edge pixels, causing them to be sharpened. For example, a value of 5 affects only neighboring pixels that have a tonal difference of 5 units or more (on a scale of 0 to 255). The default value of 0 causes all pixels in the photo to be sharpened.
This is a quick filter that can help you out when you have that image that is a bit on the soft side. It's also a filter that can be used for internet publishing, because when you scale down your images for web presentation they can come out softer. Apply this tutorial, and you're good to go.