Well Wirraway told almost everything.
I am cabin crew for another Virgin airline, which is Virgin Express, and I succeeded 4 years ago at the interviews.
At that time VEX was much funnier than now (ie uniforms, mentality...short before I applied candidates had to perform a Macarena dance !), but I can tell you how I was that day: I wore a classic trousers suit and a pony tail. No nail polish and a very light make-up. And it worked ! You don't have to look as if you were about to go at a carnival ! A boy was wearing a pair of jeans and didn't succeed for the 2nd interview.
Now some advices concerning your behaviour: always look people straight in the eyes, smile but don't exagerate, be natural, speak but not too much; if you see in your group someone who doesn't say a word, give her-him the opportunity to speak.
I was asked why I wanted to do that job. I simply told the truth: just the happiness of seeing the sun everyday at a 10 000 meters altitude; the flexible hours, the opportunity of working with different people everyday, and of course the "safety" side of the job, the customer service... I even remember that I said "I know this is my vocation, I will just feel like a fish in the ocean being a CA and I couldn't imagine doing something else".
Would you believe me If I tell you that what I said above made me succeed at Air France interviews ? Well, that's the truth but I prefered staying with VEX... Furthermore living in Paris didn't excite me that much.
Good luck to all of you who want to be part of the Virgin experience... I don't know what does
VB look like, but I really love VEX and wouldn't change airline for anything !