A lot depends on what format camera you want to use, how much space you have for the studio, and how much money you want to spend.(posted 8044 days ago)The simplest setup is a large window for light, and a big piece of white foamcore board for a reflector. Here are some examples of what can be done with this setup:
http://www.heylloyd.com/
The success of a portrait has much more to do with making the subject comfortable enough to reveal his/her character, than with fancy photo equipment.