Use a tripod. While a tripod may make it more difficult to capture different angles of some subjects, for standard business portraits, a tripod can be a huge advantage.
Many business people prefer to have a portrait for business purposes taken in their office. This provides both some context for the shot, as well as a professional look. However, unless your subject is a high ranking executive, chances are that their office will not be big enough for a full lighting setup. If you are lucky, you might be able to get away with simplified portrait lighting, but even that might be impossible in some scenarios. In that case, a tripod allows for a tack-sharp picture without the need to resort to harsh on flash lighting or a noisy ISO setting.
Finally, a critical portrait photography technique is to be sure to use flattering poses for your subject. Portrait photography poses do not have to all be the same, but certain tips can help ensure that you get the best pictures. First, be sure that the subject is facing up to the camera. Many people have a tendency to lower their head in an effort to the look into the lens. This can result in an unflattering shadow under the subject's nose, particularly on those with larger noses. Additionally, subjects looking down can create a double chin, even when one doesn't normally exist.

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For group portraits, be sure to keep everyone's heads close together lest an unforgettable space distract from an otherwise great shot. Be careful when shooting non-romantic portraits, however, that the subjects move closer together rather than tilting their heads in. Heads tilted together look romantic whether they are or not.
Above all, be sure to have fun. A tense subject is a difficult subject. If the photographer seems unworried and casual, the subject will respond accordingly. So, get your settings right and your composition setup just the way you want it, and then let loose. Remember, digital pictures are free. Shoot plenty of shots in each poses and with each look and you'll have plenty of good portraits to choose from.
Images courtesy of ArcticLlama Freelance Writing and Microsoft clipart gallery.