Exactly where the boundaries lie in areas such as phone calls, emails, emergency contact, physical touch, self-disclosure, etc.
What methodology he/she uses.
How he/she develops goals with the client and how to know when they are met.

None of these things were discussed with my current T until they arose, and I wish we had discussed them in the beginning.

This is off the top of my head...I'll come back if I think of any more.