What is a portrait? According to Wikipedia, a portrait is a painting, photograph, sculpture, or other artistic representation of a person, in which the face and its expression is predominant. I have also heard the word portrait refer to pictures of animals, like a portrait of a walrus. So beauty is not essential.
Like all photography, the key to a successful portrait is lighting. You should flatter or show the character of the subject. You can use natural lighting, continuous lighting or flash lighting or a combination. Each has its benefits, but for still photography I generally use flash. Indoors with flash lighting you can reproduce the same lighting at mid-day or mid-night and outdoors on location you can light the environment and the subject separately.
Your main light is called the “key” light and its purpose is to simulate the sun (if you aren’t actually using the sun). That means it is never below the level of the eyes and on this planet there is only one key light. Other lights are “fill” lights of various types to reduce shadows or light specific areas like the hair or eyes.
If you are using studio lighting you must embark on the single thing that will make 90% of “people who own cameras” turn into “photographers”. That is, the use of the dreaded but essential, Manual Mode. Until you have master manual mode you are merely allowing some technician in Japan to make your exposure decisions for you. You will probably also be using manual focus, at least to some extent. Having 45 Focus Points on your very expensive camera is fairly useless. The only thing in portraiture that needs to be in focus and correctly exposed are the subject’s eyes, not the tree stump she is standing next to.
Equipment wise, a “portrait” lens is a short telephoto lens 80-180mm in focal length. This is because a wide angle lens expands the distance between foreground and background giving landscapes depth. A telephoto lens compresses distance so foreground and background appear closer together. This means your subject does not have a big nose compared to her ears. Big noses created by the photographer are generally not flattering to the subject.
For this reason full frame cameras like the 5DMk2 or D700 are regarded as entry level in portraiture and especially fashion, with the real pros using medium format like Hasselblad or PhaseOne. If you put an 80 mm lens on a cropped sensor camera you will find you need to be nearly 5 metres from the subject to take a full length shot, which is an unworkable distance. With full frame you are 3 metres. A medium format will let you work 2 metres away. But don’t despair, work with what you have.
I hope that has been informative. I run a one day Studio Workshop and Model Shoot in Sydney for those interested in learning more. I also run location shoots. The next ones are on the 25 June and 2nd July around the Royal National Park. I supply the model and lighting equipment. Details at http://AspirationImages.com