I still think the hardest part of portraits isn't shooting or post-production but the human element. Making your subject feel comfortable in front of the lens is crucial to getting shots you're both happy with. This helpful video will give you some quick tips on how to do just that.
Coming to you from Pierre T. Lambert, this great video talks about what you can do to make your subjects comfortable in front of the camera. As Lambert mentions, communication is key, as you need to establish a quick rapport. To do this, I put together a list of innocuous topics to which almost any person will have a positive response and have something to say. I keep the list memorized and can fall back on it whenever the conversation or flow of a shoot begins to stagnate a bit. For example, I'll often ask if they have a best friend. When they say yes, I respond with: "think of the silliest sh** you two ever got into," which inevitably provokes a sudden burst of laughter and a genuine smile. The key is to make your subject feel less like they're in front of your camera and more like they're simply having a conversation with you.