Make sure that your recent twitter and linkedin posts are work-friendly.
Put on a nice suit. Be smart and neat.
Read about the industry, manager, and job opportunity.
Don't forget your body language like making eye contact, your posture, not fidgeting and not mumbling.
Sit down, be calm, take a few minutes to ready yourself ahead of going through the door.
Say thank you to your interviewer at the end and after by email or send a 'thank you' letter by post.
Advice for Job-hunters:
"Begin with self-assessment. The job search process begins with an identification of your values, interests, skills, accomplishments, experience, and goals. How can you seek a position if you don’t know what you want from a job and what you have to offer a prospective employer? Self-assessment, though a time-consuming process, gives invaluable information to facilitate future career decisions and to prepare you to market yourself productively."