Don't worry about hair or clothes. If you start arranging details like makeup and backdrops, the sitter will begin to feel like she's on stage. Your assignment is to capture people as they really are. Making people feel at ease is paramount. Take your work outside.
Natural light is more pleasing than harsh flashes.
Be aware of lighting. Late afternoon is the best time to shoot, because the light is warm and produces nice textures. Morning works, too. Avoid noon lighting, however. Overcast days are also good, since they produce even lighting.