Sharpening with the Unsharp Mask.

So the first thing you should do is forget about the menu options Sharpen, Sharpen More and Sharpen Edges. These are merely default settings of the Unsharp Mask. The Unsharp mask can do these things and a whole lot more.

But what is Unsharp masking? Wikipedia says...

"Unsharp masking is an image manipulation technique now familiar to many users of digital image processing software, but it seems to have been first used in Germany in the 1930s as a way of increasing the acutance, or apparent sharpness, of photographic images. The "unsharp" of the name derives from the fact that the technique uses a blurred, or "unsharp", positive to create a "mask" of the original image. The unsharped mask is then combined with the negative, creating the illusion that the resulting image is sharper than the original."

Digital Unsharp masking is a little different.

First, it increases contrast at the pixel level making dark pixels darker and light pixels lighter.
Second, it accentuates lines by searching for broader areas where light and dark tones meet and making the dark edges darker and light edges lighter.

A point to remember: Sharpening only makes the image "look" sharper. No amount of sharpening will fix motion blur. Sharpening cannot fix a significant lack of focus.
Also, sharpening should be done as a last step in your digital workflow, this is my opinion and seems to be shared by most of the digital imaging community.

So how do we go about using the Unsharp Mask tool in Photoshop?

1. The first thing we should do is view the image at 100% of the output resolution.

2. Select the area of your image you wish sharpened, or don't select anything to apply the mask to the entire image. Which one you choose will depend on your image and the results you want. If you select a part of the image, I suggest you use the 'Feather' feature from the 'Select' menu to reduce any harsh lines that may be created between your selection and the rest of the image.

3. Start the Unsharp Mask Filter by selecting the Filter menu, Sharpen and Unsharp Mask. The Unsharp Mask filter has three settings.
Amount: Controls the intensity of the effect (not the actual effect)
Radius: Is the effect. This controls the way edges are treated, how much halo effect is applied. Too much and you will lose subtle detail or your image will look unnatural.
Threshold: suppresses noise in smooth areas. The levels refer to the number of levels that need to be different for the effect to be applied. Too few, and you might have noise in your image, too many and you may suppress the sharpening effect entirely.

4. Reset the Amount, Radius, and Threshold to their lowest values (0, 0.1, 0) as below
unsharpmask

5. The settings you use will be different for each image but after playing with the settings you will find a combination that should work with most of the images you take, with a little adjustment.
a) Start by moving the Amount slider to it's maximum (500%).
b) Now set the Radius. Be very precise, but err on the side of a little more. Especially if you're going to print your image on an inkjet printer.
c) Now set the Threshold, but only if necessary. If noise is visible, or too high adjust the Threshold until the noise is at your desired level. When done, click OK.

unsharp2

d) Finally, fade the effect of the Unsharp mask to luminosity. This limits the effect to just light and dark areas without effecting colour. From the Edit menu select 'Fade Unsharp Mask' and select Luminosity from the 'Mode' menu. Adjust the 'Opacity' until you have a pleasing result.

fade

You're done. Don't forget to save your image.

Remember: If you're printing your image on an inkjet printer, be slightly aggressive with the Radius setting. This will counter the bleed that occurs as ink is absorbed by the paper. If you're outputting your image for the screen, be very precise.

Now that you know how to use the Unsharp Mask Filter, don't ever use the other options, they're a waste of time... in my opinion.

PS. Digital noise is sometimes much more evident in the Blue colour channel. You can check this by selecting the Channels Palette and then highlighting the Blue channel. Compare this with the Red and Green channels. If the noise is much higher, consider applying a slight blur to this channel only, and/or sharpening only the Red and Green channels. A simple way to do this is to apply a test sharpen to the RGB channel, take a note of the settings and apply half of the amounts to both the Red and the Green channels.

PPS. My example image is over sharpened to show the effect.