Digital Toolbox: How to Fix Spots, Dust, Tears, and Scratches

Scanning

Before you scan your shots, make sure you are in "professional mode" (or whatever your scanner calls the mode with the most features). Make a preview, then select your image on the scanner bed by drawing a box around it. Be sure you don't get any white, nonphoto space in your box, because the scanner will factor that in when it calculates your picture's tonal range.
Go to the histogram and make sure the automatic adjustment isn't clipping anything. If it is, move your black and white sliders out. It's much better to start with a flat, low-contrast scan containing lots of data than a high-contrast one that leaves some data out.
Note: This screengrab is the driver on the Epson Perfection 2450, so yours might look a little different.