Your wonderful, expressive face is the focus of these images. As such, you should wear things that complement your face. Solid, rich colors colors are ideal for theatrical headshots: charcoal grey, deep blue, deep purple, blood red. For commercial portraits, lighter, airier colors are good: white, pastel blue and pink.
It's also a good idea to wear clothes that compliment your complexion and eyes. A deep purple plays well with red hair and green eyes. Deep brown skin plays well with indigo blue. Well-made clothes photograph better than less well-made clothes. If all else fails, a nice blacks v- or scoop-neck t-shirt that fits you well may be all you need. Wear something that makes you feel good.
Hair and Make-Up
Hair should be styled simply. Less is also more when it comes to makeup. The more your makeup looks like you're not wearing makeup the better.