How to get the best out of user interviews?

Hey there 👋

I am starting to give access to the early users of the https://www.buildpublic.app/ waiting list. I added a Calendly link, so they can book a call with to have a demo and gather feedback about it 😄

What are the main questions that I should ask them?

Should I let them go around and see their behaviour without saying nothing?

Should I give some tips?

Do you use other tool apart from Calendly?

Any tip is more than welcomed 🏄‍♂️