Lea,
If the interviews are are still the same as in the years past, the first interview will be a group interview. Try to wear an outfit as close to the uniform of Virgin as possible. Of course, your appearance should be immaculate, fresh manicure and light touch of cosmetics. Avoid any heavy perfumes. Try to remain as calm as possible and pay attention. Keep your responses positive and brief without being abrupt. Tell them why you wish to work for Virgin specifically, not the usual "I love people, I love to fly". As the previous poster said, learn as much as possible about Virgin before the interview. Don't be shy about letting the recruiters know what skills you have that make you a good prospect, like experience you may have working with the public or any languages you speak.
And remember if you don't get on, try again. You could write a letter asking why you weren't selected so you can work on any perceived negatives about your presentation.
Good luck and let us know how it goes!