I filled out a job application online (be prepared to sit awhile, it takes a long time to fill out), and was called the next day for an interview. I showed up 15 minutes early, and was offered a free drink and told to wait at a table for the manager.
She eventually came and sat down with me, asked me some friendly questions about my day, pulled out a notebook and began asking me questions. Now the questions are really tough, usually asking about situations you've dealt with at different jobs, and how you handled them. At this point it helps to have the drink, so you have something to do while you think of creative answers, haha.
She ended up asking me around 10 questions, then asked me if I had any to ask her. She then provided some information about the hours they'd be hiring, and wanted to know if I was willing to work my way up in the company. Then she told me she would call me within two days if they were interested. I got a call today and they're doing a second interview at another location, apparently.
I recommend going online and trying to find some sample questions Starbucks uses so you'll be prepared. I had an idea of what they would ask, and I still had to scramble to think of answers. Try to be nice and personable, and don't freak out! I think the interview lasted around 30 minutes, so it wasn't too long.
Just do your best, and I'm sure it will go fine :D