In my personal experience, it wasn't an overwhelming interview. They asked general questions about your work experience and why you want to work at Macy's. They also asked a few situational questions where they ask how you would react to the situation. They try to hire as many people as possible for seasonal work, so don't stress too much about the interview.
The best way to prepare is to go in looking professional. I wore black pants and a nice shirt, the dress code is actually all black so that's a good way to start.
Wear comfortable shoes in case they decide to take you on a tour of the store.
They definitely like people who show initiative, who are willing to do multiple jobs and do all that they can to make the customer happy.
Another good way to prepare is to go in with a willingness to work where ever they put you. I worked in the Junior's department and that was actually the busiest in the store. You tend to be given many responsibilities so it's good to be sure they know you are willing to go out of your way to help customers first and get all other responsibilities taken care of.
I tend to be quite introverted but as long as you show an ability to speak with customers and go out of your way to help them, you'll do great!
Made sure I had my most up to date copy of my resume. Because it is a retail clothing store I put together an outfit that was up to date with fashion trends. And I went over the job description multiple times.