A good portrait brings us uncannily close to a real human being. Its impact and immediacy are such that little seems to stand between the observer and the subject. Indeed, the image approaches reality. So what are the hard-to-define special qualities that elevate the finest images to such levels? Photographers talk about pizzazz, zing and the x-factor, but what does this really mean in terms of photographing people? A definitive statement would undoubtedly be useful, but in practice there are too many different subjects, styles and techniques to consider.

However, whilst accepting that any effort in this direction will be incomplete and imperfect, there is no reason to evade the matter. So, in no particular order of merit, and complete with gaps, wrinkles and appropriate health warnings, a few suggestions follow.

• Beautiful light is virtually a prerequisite for a stunning image. Those extraordinary warm colours that pass so quickly at sunset are impossible to describe in words. Bathe a model in light of this quality and the skin becomes incandescent. Use back-lighting and the body is rimmed with gold. Alternatively, go out at dawn when the air is cool and moist, and capture the spring-like freshness of a young complexion.
• Form and texture are revealed by directional light, perhaps striking a surface at a low angle. This produces sharp contrast between light and shade. Sure winners are intimate skin texture, wrinkles, callused hands, rippling muscles, and exquisite beauty shown in fine detail. The illusion of image depth is also a product of contrast and directional light, but may be enhanced by careful use of perspective, line, shape and colour. Telephoto lenses and differential focus can be use to emphasize the separation of foreground and background.
• Atmosphere and mood add emotion and meaning to an image. Lighting that conceals detail creates mystery, and backlit smoke and dust add intimacy. Soft focus, muted colours and reduced contrast give a feeling of tranquillity, and strong light and vibrant colours are cheerful.
• Eyes certainly deserve a mention. Wide, round eyes, or those with a particularly interesting shape or direction, add magnetism to a portrait. Introduce emotions such as love, fear, joy or despair and you have an x-factor. If the eyes are sparkling, moist, intense, or focused like lasers that is also a plus.
• Vitality results from lively or mischievous eyes, from intensity, from action or movement, and from the presence of bright saturated colours. It is the feeling of expectation and immediacy produced when a subject seems about to move, and is emphasized by dynamic composition.
• Asymmetrical equilibrium is achieved when an appropriately placed secondary element balances the weight or impact of an off-centre subject. The result is a sort of tension felt throughout the image.
• Unusual positioning in the frame, particularly of the subject's eyes, may produce an unexpected quality as attention is drawn away to a corner or edge. When combined with strong lines and shapes, and implied lines such as the diagonal gaze of eyes directed to the corner of the frame, a powerful and dynamic composition is possible. Other lines, such as those suggested by the body, or a particular limb, can be used to create simple geometric shapes.
• Finally, communication encourages the viewer to feel in contact with the real subject. It is enhanced by direct eye contact, expression, a feeling of involvement, the portrayal of mood or atmosphere, and the interpretation of a message or deeper meaning.