It's not what you should reveal that you should really focus on its how you reveal it. That's what truly important.
I understand that the foundation of a good reveal is based on what piece of information you are going to reveal but the process is far more important.
Secrets, emotional memories (nice ones), feelings and private emotions, star signs, D.O.B, characteristics, the hobbies they had as children.
There is a million great things, the greatest thing to remember is that once you have revealed anyone of these things you have proven you can do what you set out to do. So from then on, everything else from that point becomes about "Try me" , "See if you can read me then" .
The knack is to reveal stuff in different ways (that are unexpected) , so it a. doesn't get boring and b. you reveal it in such a sideways sense that it leaves people wondering what you are going to do next and stays interesting at the same time (prevents head butting).