Well, for a start, having worked for for GB for a while i wouldnt advise this airline but i guess it s a good start if you havent flown before.
But dont believe what they tell during the interview, they will tell you that you night stop in amazing places etc etc
In fact i didnt night stop much that much at all. Also you will be able to choose after a while between Gatwick or heathrow preference although in fact you will still be Gatwick based. People with Heathrow preference do night stop alot more but always in the same places, Marrakech or Casablanca. Also money wise it is much better to be Heathrow (due to night stops).
When i had my interview they presented the company as a family run airline with a family spirit. To be honnest people were not that nice, especially if you dont tell you never flown before.
As for the interview itself, be yourself and revise a bit your geography as there is test on general knowledge.
Good luck.