Nothing! Like the real films, the VSCO Film 04 Velvia presets are not typically very great on pictures of people. These films are more famous for their usefulness on landscapes because of their saturated colors and high contrast. Velvia 50 will be the worst for portraits, with Velvia 100 being somewhat better and Velvia 100F being even better. But none of these films have a portrait version as the most common use of these films is landscapes.
Be sure to watch this great walkthrough video on VSCO Film 04 here: http://vsco.co/blog/vsco-film-04-walkthrough-video. Contact firstname.lastname@example.org if you have any additional questions.