Another quick, somewhat philosophical point. In my opinion, the goal of shooting a portrait is to make the subject look their best, to make a photo that *they* will feel accurately represents them. To this end, I've found it a good idea to tell people a few days in advance that you are going to come shoot. What happens is they make sure to wear clothes they like and they will do whatever they like to do with their hair. I find I like the portraits where I warn people a few days in advance over the ones where I just drag people under the lights.
This is a different type of photography than documentary photography, of course, where you are trying to capture the person as they really are, as opposed to how they present themselves. In this approach, you want to catch them in their regular clothes, doing what they are usually doing.
You can also blend these two approaches. The German photographer August Sander is a good example.
Good luck and have fun!