I had an interview earlier in Jan and will have another one in Feb.
This is how it went:
1. I haven't heard anything back yet, but he said at the end that they had until next week to get back to me, so I'm still hopeful that it will be a good response.
2. When it was time for me to ask questions, I asked about lab rotations (how it worked, and when I needed to commit to a lab), and how TA and RA worked at the school (he said that TA was for the first year and RA for the rest of the PhD). I also asked about lab size.
3. It was just me and the chair of admissions, he asked about my experience, what I wanted to gain from the PhD, why I was applying to a PhD, why I chose that particular school, and who I wanted to work with.
4. He did not ask me about the other schools that I am applying to, if he did, I would list 2 or three that had similar research opportunities so that I did not contradict myself. I think I made sure he knew I wanted to go to his school when I explained what I liked about it and how the research done there was very similar to what I'm interested in.
As I was talking to him, he was typing on the computer and told me that he was going to share all the information with the other members of the department. The interview was 30-40 min long.
I think I answered all questions fairly well, but at the same time I did not feel like he loved me either. So I'm waiting to see how things go, hopefully I hear their decision next week.
I think you should just relax a bit and maybe prepare some answers for the questions you don't think you did well.
Good luck!
