In most portrait photos, the subject's eyes look directly into the camera. Have your subject express a variety of emotions to capture a unique photograph. You could also try to have the people in the picture look at something in the frame.
One of the best ways for you to learn about photography is to study examples of how to hold your camera and work your subject during photo shoots. In addition, you can talk to someone who has been in photography for a long time to gain valuable insight on your craft.