This is class #2.
I'll show you how to do a levels adjustment in Photoshop. Of all the things you can do to enhance your images- and enhance may be the wrong word since you're really just bringing out the information that was already there- this is the most beneficial of all, and can be the easiest to do.
Now, most of the time the "auto levels" feature works fine. But often, the control you get from a manual levels adjustment can make a big difference. So if you want to do it the easy way, in Photoshop go to image-->adjustments-->auto levels. But if you want to get the most from your images, or the auto levels didn't turn out quite right, here's how to do it yourself.
Before I go into the detailed instructions, here are some before and after pics.
Before:
After:
