Get a smart suit, tie, shoes. ect
Then walk in with a high head, showing your confident, the last thing they want is somene who cant even handle an interview, nevermind officer training.
You go to shake their hand, so it shows you know what your doing,
Just the basics really, but get to know all the questions he could ask you, you dont want to be stuck saying 'umm, err' lol
But show your confident, and it should be a breeze,