I think I am going to share with you all a little something I picked up from Photoshopusertv.com that Matt showed. It is the high pass filter, which I really never know how to use and now I have a basic idea. I would suggest that you, head to Episode 222 and view this tutorial, Matt explains it way better than I.
The high pass:
Filter > Other > High Pass = I up the radius until you start getting edges, this setting is really up to you.
You will notice your image is now grey, now you will change your blend modes to soft light.
Now you will see that your image is crisper/clearer looking.
The high pass filter helps to sharpen your image. Please remember it will not work for every image, but learn to play never know what you might come up with.
WITH THE HIGH PASS FILTER
WITHOUT HIGH PASS FILTER
Not sure if you can see the difference or not, but check out Matt's Tutorial and you will be able to see it there.