Frequently Asked Questions :
How large should my digital files be?
Why convert and work in RGB instead of CMYK?
How do I color balance my image in Photoshop?
What is saturation?
How do I properly sharpen an image in Photoshop?
Good question, follow the steps outlined below.
Your image should be sized from 200 to 350 dpi, the size your going to print it. Zoom the image to 100% so that you can see every pixel in an area of your image. Convert your image to Lab color from the Image/Mode menu. Select only the Lightness channel on the Channels tab. Select Filter/Sharpen/Unsharpen Mask. Adjust the sharpness parameters without over-sharpening.
Typical values are 100% to 150%, 1 pixel to 2 pixels radius, and a level 5 threshold.
Finally, convert the image back to RGB mode.