If it's a retail position, just wear something nice.
Most of your answers are going to be "i may lack experience, but I am a quick learner and a hard worker" Say things like "my greatest strength is being punctual. I will show up on time, and won't miss work"
It probably won't take very long. Just act fairly relaxed, but speak like you would to your principal or something. Retail places just want someone who isn't brain-dead and will show up.