I hope it goes well tomorrow. As you say, all therapists are different, but in my experience the first appointment has always been about them taking some sort of history - so asking some questions about why you have chosen to see a therapist, treatments, medications and so on, without going into too much detail - and also trying to put you at your ease. When I first starting seeing my therapist where I live now - about 6 months ago - I was so relieved to find somewhere to offload that I just babbled on as much as possible and cried a lot - but when I have seen other mental health professionals for the first time before it's not always been like that. I suppose there are some that are just able to put you at your ease straight away, and others where you just don't click (I am thinking particularly of a junior psychiatrist I saw a couple of times, where I didn't feel he had any idea what I was talking about). I am from the UK, so anyone I saw there was through the National Health Service, and I sometimes think I was almost embarrassingly grateful that they agreed to see me; here in the US it's very different and I haven't quite adjusted to the fact that I'm in control of the process.

Anyway, I am starting to babble - I hope it goes well for you tomorrow - let us know how you get on.