From a technical perspective, lighting is really a key fundamental in head shots. Many different approaches, different light modifiers, different locations, etc. all help make a photo unique. Also helps define the recognizable style of any one photographer.
Every head shot photographer will instantly know this is a Peter Hurley head shot, with the distinctive Kino Flo lighting, white background and strong expression. I am proud to call Peter my mentor in the head shot business as we have worked together in LA, SF, Portland and several times in NYC. He is simply the best in the business.
Pro tip: The Kino Flows are very expensive and also not very portable, but provide an almost wrinkle free, even light. There is a new LED solution from Wescott out later this year I will take a look at in October when I am back in NYC. The Kinoflows are also super bright and make my eyes water, maybe the LED approach will be more gentle.