Portrait photography (or any genre involving people) is difficult because no matter how good your technical skills are, there's a prominent human element, and your success hinges on being proficient at working with your subjects. This great video will examine five common portrait photography mistakes to avoid.
Coming to you from Manny Ortiz, this video examines some great things to keep in mind when you're shooting portraits. Of them, I think my favorite is to not keep the camera pressed to your face constantly. Portrait work is just as much psychology as photography, and when you cover your face with a machine, you're putting a very literal barrier between you and your subject. It can be tough, as you're trying to keep track of numerous photographic parameters, but I've gotten in the habit of taking my camera away from my face after every look just to say something to my subject, even if I have no direction to give and it's just a comment of support or the like. I find it keeps them both more engaged and more comfortable in front of the camera. It's important to remember that while cameras and giant lenses are normal to us, they can feel very foreign to someone who isn't a photographer.