Be willing to work evenings and weekends, especially Sundays. Sounds obvious enough, but you'd be surprised. In fact it's an automatic no if you can't work Sundays (at least at my store)
Also you will fill out an availability sheet. Make sure it is one you can commit to, because it cannot be changed for your 1st 90 days. After you've been there awhile it's more flexible, especially if you prove to be a good employee, but the first 90 days are tough, as they are usedto lots of people who quit.
Interview is nothing to sweat about. There are actually 2 interviews and the first is done by a Team-lead... A step below management. The questions are all premade on the computer... Nothing too outstanding. Just dress "tidy" and take it seriously, even if it feels like a joke. Remember they deal with a lot of 1st timers or hard-to-employee sort of folks, and interview to the lowest denominator.