There is a veritable plethora of ways to retouch a portrait, and a lot of the time, it is a game of balancing the ultimate quality with the time spent retouching. If you really want to get into one of the most respected techniques out there, it's well worth taking the time to learn how to dodge and burn.
Coming to you from Unmesh Dinda with PiXimperfect, this excellent tutorial will show you the ins and outs of dodging and burning for retouching a portrait in Photoshop. Dodging and burning is nothing more than lightening and darkening different areas of the image, and it might surprise you to hear that one of the top techniques is so basic at its core, but it's the fundamental simplicity that makes it so powerful. By only altering luminance data, you preserve the texture of the subject's skin, an aspect that becomes problematic with a lot of other techniques. It's a tedious technique and certainly not one you want to use on large sets of photos, but if you want to see how the best beauty portraits are retouched and apply it to some of your own images, it's well worth taking the time to watch the video above.
And if you really want to dive into the power of dodging and burning, check out "Master Dodge and Burn For Beauty, Fashion, and Portrait Retouching With Michael Woloszynowicz!"