From my own experience and what I was advised when I asked the question on here, learn as much about the role you have applied for, including where the training is and how long it lasts. You will be asked about your RFA knowledge; what they do, where they operate, ship names, roles, crew sizes. You may be asked to give an example of when you have worked under pressure and when you worked as part of a team. You will probably also be asked why the RFA and why the role you have chosen.
Thought my interview went ok, but I've just came home to a hammer blow because my local GP practice have left a message on my phone telling me they've given me the wrong NHS number which I've put on my medical form. So I've had it by the looks of it. :-(