Instructions
Offer to provide your subject with prints from the shoot.
Ask your subject what type of pictures he wants. Having someone who is committed to the photo shoot and is open to ideas and direction will bring the best results.
Encourage your subject to bring other friends or family to be involved in the picture. A lone subject can feel pressured and insecure, but more people in the picture can reduce that likelihood.
Tell your subject to pick the shoot location and allow her to pick her clothes. When she feels comfortable in her surroundings and confident in her wardrobe, it'll come through in her posture.