Hi Tom,
Yea like James already said, do some practice questions, make sure you know all the knowledge stuff 100%. If you don't you won't be able to be confident in the interview. Know exactly why you want to join, and when given the opportunity, demonstrate the officer/leadership qualities through examples from your past.
Other than that, just relax and be confident, and be yourself (easier said than done I know, esp in an interview).
Good luck buddy.