IMO...besides knowing about the company your interviewing for:
1 Speak when asked to speak. Answer questions and do not try to "show boat" how great you feel you are.
2. At least once in the first few minutes offer a light bit of soft humor with a smile. (This shows you are human. LOL)
3. Be humble. State you realize that you are eager to learn how their company works and become a productive MEMBER of their team.
4. Send and Email thank you (keep it simple) ASAP.
IMO...Employers want trainable people when they hire, keep that in mind.
Good Luck
Zabe
Don't worry, be happy. Meher Baba