Wow, that's different, mine usually waits to see if there is something that I want to talk about. After we sit down, I'm asked how I'm doing, if not OK, we'll talk about that. Then she asks what I want to talk about. If I don't respond with a topic or situation, she attempts to find one by asking about different parts of life, issues, or things from last session.

My idea would be that when you first get there and start, tell them that you would like to talk about X so they know what to focus on. If it starts to wander away, just to say, "I still had a question/was confused about what you said about X or had a question about it".