Well, I didn't even have an interview. Here's how I skipped that whole process; I sent in my application in spring when the place wasn't too busy..and waited until summer (when I knew they would be needing extra help). I asked the manager (she played a big part too, because she talked to the owner for me) if they needed any help, and I gave her my number and told her I sent in an application. You shouldn't worry too much, Subway is a laid-back place and the people are usually cool. You might be like me and not even have an interview.
If so, just say you are people friendly, you work fast, and have [insert experience here]. Really, it's just a dolled-up fast food joint so don't feel nervous.