Photoshop Tip No.1 (Sharpening and Image)

The best way I have found to sharpen a full color image is to first convert the image to LAB color.
In the Channels palette, you will notice the you have 3 different channels. (Lighten, A and B)
All of the detail information is stored in the Lighten channel. Use the unsharp mask on the Lighten channel, changing the settings as needed. Convert the image back to CMYK or RGB and you will be able to see a noticable difference.
This can also be done in CMYK using the same filter on the Black Channel.