I've always been a very private, introverted person presenting male to the world. In my first session, the doctor already had some notes on me, as I was connected to him via my HMO support services after I had made an initial phone call to their hotline, and was talked down by the contact person. (Yeah, that bad.)
That made it a little easier, I suppose. I got the 'this is a safe place' spiel, and then the dam broke and I cut loose. It was insanely intense and difficult for me, but also a tremendous relief. I tried to be as completely honest as possible about everything, which was hard after so many decades of the masquerade. Still, I felt better, drained, but better at the end of the session.
I presented as female at my second session, and never looked back. I've tried to be as open as possible about my feelings and events in my life. It's not easy, but it is good to know that I can share all this stuff with someone who's not all judgemental.