@00:36One thing you may notice is that I don't work on single isolated areas at a time (ie; an eye and then move on to paint the mouth, then the other eye etc.). I like to even out my tones and highlights over the entire image before I tighten all the detail.
Here is my time-lapsed video of the process I go through when painting a portrait in Photoshop CS5 with my WACOM tablet, using mainly the airbrush and some customized texture brushes.
Also a nice demonstration of David Nagel's Photoshop Skin texture brushes which I cherish so dearly! They're fantastic for blending tones together while keeping the texture of the skin intact and looking real.
Final:
Feel free to download for a higher quality picture! It's pretty hard to see the small detail and texture after the video gets compressed.
I like to even out my tones and highlights over the entire image before I tighten all the detail.