I used to do a bunch of these... they were a great time!
Go in with an open mind. As it was already said, you will have a booklet with your background and some basic info. You will find out that you are probably a pretty shady character (along with everyone else)... you learn a little more about yourself and a little bit of dirt on others as you go along.
Just go with the flow.
I personally didn't like to come out guns blazing and accuse everyone else... then have no ammo left when the attention circled back to me.
Have a great time!