Remember that you should be interviewing them as much as they’re interviewing you. Ask questions, not due the sake of asking them, but to find out if they’re a good fit for you (so the questions depend on what you care about). You might ask things like how many hours of OT a typical employee does, or what percent of turnover the area you’re interviewing for has typically experienced.

Otherwise, be professional but try to have a relaxed conversation as much as possible.