There are a mess of books available which discuss the basics of portrait lighting. As a minimum, you need two or three lights and a background. It's also nice to have a lens with a long-enough FL that you're not in the subject's face and a large-enough aperture that you can use to blur the background. You can also learn a lot by going to the local shopping mall and making friends with someone in the portrait shop there.
The biggest problem in good portraiture is not the lighting, though. Anyone can take a picture of Aunt Maggie so that someone who knows Aunt Maggie will recognize her. It is a different thing entirely, though, to photograph Aunt Maggie in such a way that someone who has never met her will look at the portrait and feel that they have learned something about her character. That, to me, is a great portrait. A magnificent example is the portrait of the jurist in Steichen's 'The Family of Man' exhibit.