Hiya,
My transition was through the NHS. I went direct to my GID clinic through my doctor. When I had my initial appointment with the Doctor at the GID I went as female, they asked me my details, age, health, etc. Then some background stuff like cross dressing, when I first felt different, any sexual nature to the dressing, NOOOOOOOOOOOOOO. I spoke about my past a lot and how I felt back then. My then current relationship and intimacy.
Be honest and be yourself. BTW if you don't mind me asking, where will you be attending? You can pm me if you want rather than saying on a public forum.
Hope it goes well.
Stardust