This was my first job out of high school, so I went in to the store and they told me to apply online. I did, and the next day, I got a call from one of the store's managers. She asked me if I would be able to come in the next day to have a one on one interview. I said yes, and did. I met with the sales manager. He asked me some basic questions about home theater (since that was my department of choice), like 'what is the downside of full-screen DVDs?', 'what is the difference between dolby surround and dolby digital?' Do a little research on the department you want to work. You don't need to know much to start--you'll learn quickly. But learn what cameras are popular, learn what computers are selling, know your TV-makers. It'll make you versatile.
It went well, and I was called back for a second interview a week later. I interviewed with the sales manager again. He told me that normally, I'd have a third interview with the general manager, but that he was going to extend me an offer right then. I took it, and so it went.