choose a lens focal length that allows you to be about 2-3m from your subject (too close causes big noses, etc)
preferably use a lens with aperture f/2.8 or wider to allow you to blur the background
if outdoors and your lens is f/4.0 or wider, use a polarising filter or ND filter as this will allow wide apertures in bright sunlight or when using flash
if outdoors, look for flattering light - eg. under a bridge, verandah, tree, etc.
choose a wide aperture if possible to blur the background and accentuate your subject
choose a relatively dark simple background that will not detract from your subject, and avoid poles growing out of heads.
consider using your camera flash as a fill-in by setting the flash exposure to minus 2/3rds stop (“EV”), this will also add catchlights to the subject's eyes.
where possible the subject should wear long sleeves to emphasise the face
faces are generally most flattering when they are 3/4 on to the camera so that the nose does not cut the opposite cheek and you can still see the opposite eye
the main light on the face is generally best coming from a wide light source about 45deg angle to the face causing either a shadow under the nose, or the nose shadow angling down to the end of the lip without crossing over it.
nose shadow towards camera = “short lit” - nice for children, brides
nose shadow away from camera = “broad lit” - helps subdue blemishes and widen a narrow face.
camera at eye level is usually best for head and shoulders portraits
lowering it a little accentuates nose but de-emphasises forehead/scalp.
elevating the camera is often used in self-portraits of young ladies, and can enhance a short up-turned nose.
focus the lens upon the subject's eyes