think carefully on how the subject is to be portrayed:
serious
authoritative
happy
approachable
choose background (preferably non-distracting) and lighting
smiling showing teeth makes the person look more friendly and approachable than a closed mouth
jackets can look too authoritative and less approachable, consider a plain black top or business shirt instead, either way, avoid short sleeves
choose solid colors which contrast with skin tone (avoid beige, pale tones, etc) but avoid very bright colors such as bright red, yellow or orange
be minimalistic with jewellery and makeup
avoid crossing arms as this is less friendly