Every HR intern position is unique. For example, I worked on the Business Partner team and much of what I did was create accommodation reports (maternity leaves, immigration VISAs), conduct Exit Interviews, Update coworker handbook, analyze data turnover trends etc.. some other HR interns worked on job description projects, audits etc.
My biggest piece of advice is to know the company you are applying for inside and out. Also, be passionate about the position you are applying for- I love helping people which was what initially drew me to HR, I want to make a lasting impact on a company and its employees, and I made sure to convey that during my interview. I also made sure to highlight my key experiences that would be valuable to the position, for example, I interned at a law firm in the past, and I made sure to highlight that experience because my intern position worked closely with the companies attornies.
The interview process was standard and I was asked behavioral questions. As cliche as it might sound, just be yourself.