Just start by showing up. That's a big accompolishment in itself if you go when you are feeling nervous to go.
It will likely be a lot easier than you think. Feel free to let he or she know that you are feeling nervous and uncomfortable. It won't be nearly as bad as you think it will be. It's simply fear of the unknown, which we all pretty much have.
You'll be right when you get there.
Remember why you are going and focus on those issues. So if he/she says something not related to that, steer them back to your purpose. You'll get more out of it & eventually feel like you've accomplished a goal rather than just talking aimlessly.
You know it is a good counselor when you let them lead you. Wait til you get their and what needs to come out will. If nothing important comes out, time to find a better counselor. Usually they will ask you questions if you don't talk.
With the first thought on your mind. Stuff will roll forward from there, and you'll eventually get to everything.