Make sure that everything you say has substance. Answer questions clearly and concisely. Never say you cannot do something, say you are a quick, willing learner. Show enthusiasm about areas that interest you. Maintain your integrity and professionalism at all times - do not talk negatively of previous employers.
Negative words can get around easily.
Your last impression can be as important as your first impression. Repeat your strong skills and qualifications and let them know you are convinced that you would be able to do the job well. Ask for the job. Shake hands before you leave. Make arrangements for the next step.