This may seem a very subtle point, but it immediately establishes a comfortable atmosphere. Don't ignore the person who takes you in to the interview. Many interviewers ask their secretary or receptionist what they thought of the applicant. It is also important to learn the interviewer's name. Use it more than once during the interview.
People like to hear the sound of their name.
How you sound is just as important as how you look when you apply for a job. Try to identify any 'wince' words you might use, such as 'you know'. Ask a friend, a family member, or a teacher, to help you spot your mistakes. Tune your ears to them and work at eliminating them. Another important part of communication is good listening.