Sharpening a photo digitally can be a helpful way to bring out the textures in a soft image, but sharpening too much can create an annoying 'ghost' effect around hard lines. Here's a better way to do it in Photoshop without overemphasising the hard edges. In this video from photographer Jimmy McIntyre, he demonstrates how to create a mask that will target the edges in an image that you actually don't want to enhance very much. That way, you can apply sharpening to the portions of the photo that will most benefit from it. Conveniently, McIntyre created a Photoshop action that you can download on his site so you don't actually have to do any of the work. You'll still benefit from seeing how it works in the above video though; essentially he uses the "find edges" filter to mask out the edges in the photo that are already sharp.
Although the preset action is specific to Photoshop, you can probably achieve a similar effect in comparable photo-editing software.