Don't forget your body language such as making good eye contact, your posture, not fidgeting and not mumbling.
Ask good questions to demonstrate you are interested and have researched.
Thank the interviewer(s) in person, by email or by post. Common courtesy, alongside politeness really helps in interviews.
Consider your answers. You shouldn't feel pressure to answer rapidly.
Keep your words work-safe during the interview.
Job Hunting Tips:
"The bulk of people unhappy with their job think they can't take time from 'family time' or their energy-sapping job. No matter what the defence, the effect is exactly the same. Any jobseeking will fade out and you will miss the chance of primary events."