Dont over think the questions, give a complete answer and then STOP TALKING. Its ok to sit there silently after you answer questions while they take notes. Some people will continue talking out of nerviousness and hang themselves. Read up on the history of the department, know the names of the Capt, Lt., Sgt. ect., any other important stats/info on the department ex. Mission/Values. If they give you any material to read before hand you should probbably do your best to remember it for the interview. Keep in mind that they want to know about you more than anything else, you should have all the answers.
Good luck.