Yes I usually know at least one thing I want to talk about during the session and since my T seems to follow my lead that is usually the first thing we'll talk about. I have had that experience that something from the small talk at the very beginning will turn into a longer discussion and sometimes it is good and sometimes its not. My least favorite is when we stay on one topic the whole time because I start to feel like I'm repeating myself. When I feel this is happening I have to literally say, "OK enough about that, let's change the subject." I don't think she has ever asked me questions about something we discussed in the previous session. Even if I don't have much to say in the beginning she will just wait. I don't know why but sometimes this bugs me. I guess I wonder sometimes if she even remembers what we talked about last time. Possibly not considering how many people she talks to every week. That would be a lot of details to keep track of and you certainly won't want your T to mix up something you said with something someone else said.
As far as lying goes I have the same problem as JM. I am a terrible liar so I haven't told any big lies. Like AG mentioned, if I lied what would be the point of paying for therapy? I have definitely glossed over some details and once flat out refused to answer one of her questions. Because I can so quickly feel embarrassed or ashamed even about a trivial detail I do what I have to do sometimes in order to just get the words out.
Right now I have a few things that I don't ever want to admit to and am foolish enough to think that I'll never have to. But I also know that eventually everything comes out in therapy if you stick with it long enough. Hopefully by then I would be so imprisoned in shame and I'll just laugh about it.