JKS already gave some damn solid advice, so I probably can't add much more to that.

I've taken a few oral boards, so to echo some of the things that he already said: The ones that I've done were a panel of people, mainly consisting of officers in a Supervisory capacity. I'd say the most important thing and I know it's easier said than done, but do your best to relax. Be honest. The sample questions that JKS gave were similar to ones that I was asked, especially the one about seeing a fellow officer doing something illegal. When asked what I would do, I was honest....I said that I'd bring his actions to the attention of the supervisor. The guy who asked me that question said, "So you're telling me that you'd turn in one of your fellow officers, the guy who you work with, the guy who's locker is next to yours. You'd turn him in??" I dont know if that was the nail in the coffin, so to speak...lol...as one of the reasons why I didn't progress from that point...lol...but I was honest. Deep down, I'd like to think that the answer I gave was the right one. I mean, who the hell wants to work with a dirtbag? LOL.
Of course, there will be decision making situations as well. While I'd like to think that if faced with the multiple call scenario, the Sgt on duty would be directing people where to go, if you were faced with those same situations, I would reroute to the lost child, followed by the officer assistance, then the larceny. **This is what I would do. I'm not saying this is the right answer.**
Dress: Suit and tie. Be on time. I'd arrive at least 15-20min early. If you're not familiar with the location of the interview, definately do a trial run prior to the actual day.
Good luck! I'm sure you'll do fine.
