Portrait Lighting
Shoot in natural, even light. The ideal location for a portrait session is outdoors in early morning or late afternoon, when the sun will be bright enough to create a quality image, but not so bright that it creates shadows. Use the flash, which will help to highlight the facial features in natural light.
If you are shooting inside, avoid using the flash. Indoor lighting that is too dim will not result in a good photo even with the flash. Additionally, the flash may create awkward shadows or wash out your subject.
Portrait Focus
Novice photographers are often tempted to capture beautiful scenery or interesting decorations around their subjects, but these detract from a portrait shot. Your subject's face should take up the majority of the photo and there should be little or no additional space around your subject.
Realism Versus Staging
There are different perspectives on whether or not portrait photos should be posed. Some photographers take a photojournalistic approach and attempt to capture candid moments and faces. More traditional photographers aim for quality in their images and may be less interested in realism. Try to capture a combination of staged photos and candid moments. If, for example, your subject's dog walks by, snap a photo or two of her looking at the dog.
Posing
Unless you're trying to capture a candid photo, it's important that your subject is posed in the most attractive and natural way possible. Photos of the entire body often result in awkward, stiff limbs. Carefully observe the way your subject is moving and make adjustments as necessary. Ask your subject to move her head slightly to the left, to bend her arm or to make other adjustments that will make for a higher quality photo. Avoid photographing from either underneath or above your subjects. These angles can cause unattractive photos.
Background
A solid-colored background will generally result in a higher quality portrait photo. Consider using a photographer's backdrop for a more uniform look to the photo.
Editing
Most professional photographers use photo-editing software to improve the quality of their images. These valuable tools can turn a mediocre image into a stellar one. Consider turning up the brightness on a dull photo, turning up the contrast for a more stark image and eliminating or adding shadows to suit the mood of the photo.