My First Job Interview.?

So I have my first job interview tomorrow and Im really nervous. I dont know what to wear. and im nervous about the types of questions theyll ask me... Im 15 btw. Its a new store opening i think, I replied to the job on craigslist and they told me to come over for an interview. and they sounded kind of in the need for employees badly so i think i might get the job, but im still nervous. any help would be appreciated