It can be useful to go on a couple of practice interviews first - Interviews for jobs you don't really want but are qualified for so you get a bit of practice at the interview process. Obviously you treat them as if you are interested and who knows, maybe you might be ultimately more interested than you initially thought. That will help work out some of the nervousness by the time you get to your dream job... OP, we all are nervous to some degree on an interview and sometimes do or say dumb things. A good interviewer will try to put the candidate more at ease with some general talk at first so they can get a better judgement of the candidate's skills and not so much their initial nervousness.

It's totally the interviewer's fault for being so unprofessional as to bring soda to a job interview. :D