I managed to win tickets to the London premiere of Red Riding Hood, but have no idea what to wear! Any ideas?

I don't want to be too underdressed or overdressed. I'm not famous or anything. I'm a girl so I was thinking maybe a dress, but didn't know whether a casual one would be good like a summerdress or a maxi dress or LBD would be better. Or do you guys think I'm completely wrong and jeans are the best bet? Thanks!