The best way that I have found to sharpen an image was through a Photoshop lesson from Chris Orwig.
After everything in your photo has been corrected you will want to place all the items into their own group. I typically call them “Enhancement”.
In Windows I hit “CTRL+ALT+SHIFT+E” to make a new layer that a is the equivalent of all the layers merged into one.
While the top layer is selected you will want to click on “Filter-OTHER-High Pass…”
You will get a “High Pass” dialogue box pop up. Play with the radius. What’s nice about this technique is that it is better to add too much then too little. Click “OK” to apply the “high pass”.
Now hit “CTRL+SHIFT+U” to de-saturate the layer. This will make sure that the picture is only grey colors.
Now this is where things get interesting.
Make sure the top “high pass” layer is selected. You will need to apply a blend mode to the entire layer. I find “Soft light” produces the best results.
Now if the image is too sharp you can use the opacity of the layer to “decrease” the amount of sharpening by dialing it in to however you like.
The second way:
is by using the same key combo to merge all the layers up to the top later (CTRL+ALT+SHIFT+E").
Turning the layer into a smart layer and then applying unsharp mask. Using the dials you can change the sharpening at any time.
Make the changes as needed.
Again since this is on it’s own later you can finely control the amount of sharpening either by the filter controls or through the opacity.