(1) Have good reasons why you want to be in the RAF
(2) Have good reasons why you want to be an Engineer
(3) Know what an RAF Engineering officer does.
(4) Know where the RAF is around the world, what it's doing, and why
(5) Know what kit the RAF uses, and something of its engineering
(6) Know about the political background to the RAF (budgets, acquisitions, any recent scandals)
(7) Have some good reasons why the RAF would want you in it (personality, hardworking, lifelong belief in it, county Rugby player...)
(8) Practice being interviewed - get a friend, teacher, parent, etc. to try interviewing you on these topics, tape record it, play it back, try again and do it better.
(9) Relax and enjoy it!
G