Do some research about the history of the company/organization you are going to work for. I did panel interviews for multiple police departments a while back and made the top 10% in all of them. My last interview, I was placed as #6 out of 56 applicants.

For the cities I applied with, I learned the basic history of the city, history of the department, notable incidences, officers who were killed on duty, important people or incidents about the city or people in it, etc.

I also prepped myself for integrity-based questions.

Example: "You are with your training officer at the store and you witness him pocket a candy bar. What do you do?"

Most people in this situation give really bad answers like "I don't care, he's a cop, he can do what he wants" or "I would arrest him immediately and haul him in to the station!"

Correct answer: Wait until you are somewhere private and ask whether the pocketing of the candy bar was accidental or on purpose. If he states it was a mistake; no big deal. If tells you to mind your own business, speak to his supervisor.

Doing mock interviews with friends or family is extremely important, especially if you are on the shy side. Don't overthink questions and try to give somewhat basic answers; they don't need a 6 page essay on how you feel about a given subject.

And for the love of god. At the end of a panel they will always ask "Do you have any questions for us?" Always ask a question. ALWAYS. Ask about a current event with the company or the future of the company or about something unique with the company or its community involvement etc...

Dress nice. If this is for a professional company, wear a well-tailored suit and tie; even if it's for a company where the normal wear is casual. You will stand out and if that suit looks real good, you will stand out that much more. Don't over-do it with the cologne tho. Neutral or mild smells are good.