Be prepared: you WILL be hit with questions back to back, with many of them turning out to be irrelevant to the job. I was interviewed by two people: one that asked the questions, and the other that simply sat there and stared me down, making me feel very uncomfortable. The interview took place in the smallest meeting room imaginable and honestly felt more like an interrogation.
After nearly a half hour of questions that involved answers I would need to be trained for, I was given a written test on my abilities with shelving via the Dewey Decimal System. Once I turned the paper in, I was told that I would receive an email about whether I got a job offer or not, and sent on my way.
I did get the job, and I can easily tell you that the interview for this particular position needs to have an overhaul. So many young teenagers and even adults will be scared off of this (very much) entry level position due to the grueling formality of the interview process.