Say thank you to your interviewer at the end and after by email or send a 'thank you' card by post.
Do not go off topic. Keep your thoughts on the things you are good at.
Read up on the company, owner, and job opportunity.
Interact, maybe, with the interviewer's linkedin profile.
Do not use unprofessional terminology.
Learn regularly asked questions and rehearse your replies.
Put on a clean suit. Wear it sharp and clean.
Suggestions for those looking for employment:
"Proofread! When you are proofreading your CV, have one or two other people read it also before you show it to a potential employer. Sometimes when you work on something for a long time your brain can automatically make changes and correct what you are reading without you even realising it. Spell check is not infallible and cannot discern between words like wood and would for example."