I did a couple of model head shots when I had that model photo shoot weeks ago. Head shots are pretty simple to do. It is one of the most fun parts in portrait photography. It was actually the highlight of that day.
When doing head shots, I prefer using a longer lens. A longer lens doesn't give you bad distortion in the models face. You know you have bad distortion when your models nose becomes pulled in towards the center of the frame. Giving it a larger than what it's supposed to be look, a very common error for head shots. The longer lens also gives you breathing room between you and the model. Models usually don't like it when there's this huge camera less than 2 feet away pointed at their faces. The extra breathing room a longer lens provides makes the model feel at ease.
For this shot I used my 70-200 lens. The distance between me and the model gives me that perfect frame. For this shoot I used my favorite beauty dish for the top light, and a strobe with a softbox below the models face. I then used strobes for the background, overpowered to blow out the highlights in the background. The beauty dish gives the models a punchier light than a softbox without burning the highlights...as I've said before, you can't live without one for portraits.
The rest of the shoot was just plain fun. We were making the models laugh while shooting them. Making the photos look more natural than real staged ones.