It depends on the job. My biggest recommendations:
- Be you! You'll find the exact right fit between being professional and being yourself with time. It really just takes repetition to find the mix. I do find that the most successful interviewers are people who are honest about their passions.
- Research the people who are interviewing you on LinkedIn. It shows them an exceptional level of preparation and tells you a lot about the job.
- Failure is an option. Interviews are all about finding fit. I have had about 60 interviews for different positions. You don't always get the job, and you don't always love the company. If you're ok with that, it helps take the pressure off performing in the interview.
Best of luck!