Not really, just cover all your bases. I wnt back in 96 and again in 98, and both times were totally different. Make sure you at least know what the basics are of all wars etc, especially recent ones, and why - look at both sides of an argument, that way it looks like you've used your head and have an opinion....that way they'll move on to something else, as they want to put you under pressure. they're not there to trick you, but deffinately to see how you react under pressure, infact they even have one person asking the q's and another sitting there marking your reactions to them. Be clued up about who's in the various things like the UN etc and who is going to join.
the best advise I was given, and it's true, is ...don't BS them, they are professionals at sniffing it out!...if you don't know, then just say so!....it shows strength of character.
Also, always know the end of your sentence before you open your mouth to start it!
Best of luck, and remember, they're only human, not monsters!!...so don't be intimidated, but don't act cocky either!