woskam
You can't really prepare for it. Perhaps have a look at a picture of a 737 flight deck and be able to identify the main controls/displays. The best thing you can do is relax, ask lots of questions, tell the captain when you've realised you've done something wrong in the sim, and enjoy yourself!
It's an awesome day.
In terms of experience... I spoke to two guys at phase 4 who had made it there with zero hours. Not even a trial lesson. Just shows..