At last! A transition-related thing I can speak on with some authority, having actually done it!

I know it's nerve wracking, especially if there isn't a lot of choice in your area... what if you don't like them, what if they don't like you? What if they reject the notion that you're trans? All these and more were running through my head, and the actual experience was a very pleasant surprise. We had a gentle conversation, regarding why I was there, what her experience with trans people was, etc. I told her honestly that I had done a lot of soul searching, told her about my previous therapy, where I was coming from, background information about my life.
Ideally, it would be good to ask your therapist about her or his experience with transgender people before sitting down with them for the first meeting (Have you known anyone personally who transitioned? -- always good to know if they have been there through all aspects of a transition or twenty). The first session is often the free "getting to know you" session anyway, so feel free to ask anything. If a therapist is going to be successful, they need to develop rapport with their patient, so they will generally be happy to answer your questions. It's kind of like a job interview, for them. Remember, you have some power here, too; you can always find another therapist.
That's another thing. From the outside, they seem like the all-powerful gatekeepers to the magic kingdom of hormones and SRS and, to a certain extent, they are... but from their perspective they are genuinely trying to help someone (you) come to terms with your gender identity and dysphoria and help make you well. They *want* to help you, otherwise there are higher paying jobs they could get with their degree.
If you get a therapist that won't answer questions, doesn't click with you, doesn't have experience in the area you need, *you* have the power to fire them on the spot. Remembering that can help.
Ideally you'll come out of the appointment feeling confident in your therapist and her or his ability to help you through the process... and that's a big step. A great start.

*hug* Good luck, sister!