One of the first things to realize is that in taking photos of people you have entered the world where your photo is no longer 100 percent in your control. You are now in a collaboration with the model. The way that you make the model looks will be the most important part of the photo.
The photographers that work the best with models generally are good with people. They have a great amount of patience and can really work well with other people of different types. Not all models are the same. Some will be very short of their attention whereas others will simply be tired and complain all the time. Some models will also be somewhat withdrawn and take some warming up before they can take good shots. Unless you are a professional photographer that can stand to accept only the best models you are going to have to learn to deal with these problems. You want to make the model you are taking pictures of to be as unstressed and comfortable as you can.
When you take a picture of a person you want to capture the part of that person that you know that person wants everyone else to like about them. If a person has a very fun and happy personality try to show that in your image. Most likely you are going to be going for a photo of a person that is happy. There are serious pictures as well that you can take but for the most part the happy pose will work.
When taking pictures of people smiling and laughing, the best way to take it is to actually have the laugh and smile be authentic. Contrived facial expressions can come out looking very fake unless the model is very well trained.
A critically important part of pictures of people is the background. First off, ask yourself if the background is contributing to the photo or not. Is the background helping you know more about the person? Of course, not all backgrounds can be used like this. Sometimes using a background color that makes the models skin color stand out will be fine.
Another big part of people shots is how they are lit. When you light your people being photographed you want them to look as pleasing as possible. Mostly using lighting that is from the front will work best. This type of lighting will help to lessen skin blemishes.
Overall, taking photos of people is not that difficult. The most important things to remember are to make the photos realistic. Do not try complex poses to make the photo look better if it is going to make the person look unauthentic and uncomfortable.