Anticipate Behavior
Knowing when to press the shutter button is a critical part of a photographer's skill. Learn to anticipate a subject's behavior by paying close attention to their mannerisms, hand gestures and facial expressions. If you know that the subject tends to crack a large smile just before a fit of laughter, you'll be able to capture it more effectively. The more time you spend with the person, the better you'll become at reading and recording their expressive nuances.
Interact With Your Subject
Many amateur photographers make the mistake of silencing themselves behind the lens. This is often a result of nervousness or shyness, especially when photographing strangers. Learn to talk through your viewfinder -- tell jokes, ask the subject about their day or chat about a current news story. This involves the subject in the photographic experience and will provide casual, natural looking portraits as a result.
Make it Environmental
Environmental portraits position the subject within a scene, making them part of it instead of excluding them from it. Although the subject tends to be the focal point of any portrait, inclusion of setting elements can reveal much more about them. For example, a portrait of a local fisherman will be more effective if you position him on the edge of his favorite dock, or in front of the bait shop he frequents.
Get Abstract
A portrait need not include a subject's face if there are other interesting details about them. The wrinkles in your grandmother's hands or the worn, tattered shoes of a skateboarder can reveal just as much about a person as a grin or fleeting glance. When shooting details of this sort, move in close and pay attention to framing and composition. When paired with a facial portrait of the same subject, these pictures serve as excellent storytellers.