Image sharpening is one of the most important steps in a postproduction workflow. However, with a myriad of options and methods to do it, it can be a daunting understanding exactly what you're doing and why. This great tutorial will show both what sharpening an image does and how to do it.
If you look at the images from most of your favorite portrait photographers, they likely all have one thing in common: they're sharp. In this video from Photoshop Training Channel, Jesus Ramirez walks us through the various methods of increasing the sharpness of an image in Photoshop. Like pretty much all things related to postproduction, the key to success is moderation, as overdoing it can look gaudy and fake. Be sure to pay attention to how Ramirez hones in on specific areas of the image that he'd like to sharpen to draw attention there and to avoid creating artifacts in other areas. And as always (but particularly with sharpening, I find), if you're staring at your screen for a while, trying to get it just right, step away for five minutes and come back later; you'll have a much better idea of how much more or less you need.