Here are some tips: 

• Address the interviewer/s by name.
• Thank them for the interview and for discussing the position with you.
• Express your interest in the position once again and reassert that you believe your qualifications are a good match for the position – write 2-3 sentences explaining why.
• If the interviewer mentioned a specific skill that is very important for this position (i.e. people skills, etc.), give a brief example that shows you have these skills.
• If they ask you for additional documents (i.e. list of references) this is the place to include them, and mention that you have attached them to your email.
• Thank them for their time and consideration and say that you hope to hear from them soon.