Practice. I am an extremely unsocial person typically and I have had to both do and give an interview. The best advice is to know what you will need to say and be prepared. If you know everything then you shouldn't worry, if you don't then learn. Find someone who is willing to help you out and do mock interviews with them, or even ask the owner if they are willing to help since it is a two person job. Also remember that the interview is focused on the interviewee, they are most likely more nervous then you are. One last thing is to not think too much into it, if the interview is informal speak casually on a level that everyone can understand and relate to.