Prepare your subject. Discuss wardrobe choices and locations (if being shot outside of a studio) before the shoot. The subject may wish to bring several wardrobe options, particularly if there is more than one location involved.
At the shoot, select a background which is not too distracting or which can be softened by a shallow depth of field on the camera. The background should complement the subject; avoid loud textures or patterns.
Pose the subject. Shooting a headshot with the subject's face at a 90 degree angle to the camera is an unfortunate mistake, as it results in a skewed perspective. Choose an angled pose, and try angling the head and body slightly.
Correct the lighting, if necessary. This may require the use of a flash unit or reflector to bounce light onto the subject to remove any unflattering shadows.
When the shoot is finished, process the images. Headshots should not have many Photoshop effects or gimmicks used, as these will detract from the subject. A simple adjustment to color or black and white images is all that is necessary.