Okay, first thing you want to do is open your image in Photoshop. I'm using PS8, but any version should be able to do this.
Now, go to image-->adjustments-->levels. You'll see this histogram pop up.
The histogram is a "map" of your image's light and dark areas. The arrows underneath represent the viewable range. We want to modify that range. On the left is the "darkness" of the photo, on the right, the "light" areas. The area in the middle represents the midtones. If I've just jumped over your head, don;t sweat it. Follow these instructions and it'll all make sense.
Now, what we want to do is get rid of those "dead zones" to the left and right of the black (for lack of a better word) "hump." In the image below, I've drawn two blue lines.
Move the arrow farthest to the left up to the first blue line. Move the arrow farthest to the right to the second blue line.
Just like this:
Now, move the middle arrow slightly back and forth and watch your image change. This midtone adjustment makes a big difference, and it's really up to you and how much contrast you like in your images.
Now, click "OK" when you're happy. Here's the result.
Now that was easy, wasn't it? No? Then go try it a few times. You'll get the hang of it in no time... promise. Just move those arrows to cut out the dead space and watch your image change. Experiment and have fun, dammit, this is a hobby!
Travis