When sharpening an image for presentation the easiest thing to do would be to choose Filter-->Sharpen-->Sharpen. However, there's no control over the results and generally your photo will be over-sharpened to the point of looking jaggy. You can "fade" the Sharpen effect here by choosing Edit-->Fade Sharpen but you have to guess at the percentage you want to change the sharpening, and this might take awhile to decide.

I don't pretend to know the capabilities of all the Sharpening tools in the Filter dropdown menu; there's Sharpen Edges, which seems to choose the highlights to sharpen; Sharpen More, which is even more extreme than just Sharpen; and Smart Sharpen, which can do wonderful work on an image and is worth its own tutorial by some enterprise-minded Photoshop fiend.

My tool of choice is File-->Sharpen-->Unsharp Mask. It seems to be the easiest way to find the right balance between crispness and softness in an image. Try it on an image of yours. When you choose it, you'll be confronted with a dialogue box. Type in these settings and see what you think: Amount: 50%. Radius: 1.0 pixels. Threshold: 0. You can experiment as much as you like, of course, to get the most pleasing result.

I just discovered (via PhotoshopTV) a great addendum to this hint. Open your image, which is more than likely in RGB mode. Convert it to Lab Color by choosing Image-->Mode-->Lab Color. Then, in the Channels Window (activated via Window-->Channels) click on Lightness and then apply the Unsharp Mask filter. Convert back to RGB, and you'll see a difference in the quality of the sharpness. By choosing to work just on the light parts of the image, it really sets it off against the darker.

Here's an image where I've applied the Unsharp Mask filter at the settings mentioned above: RGB.
And here's the same image opened in Lab Color and then the same Unsharp Mask settings: Lab Color. What do you think?

If you have your own methods for sharpening an image for presentation I'd love it if you shared them in the comments below. Please focus on sharpening, though--save other hints for future posts!