Prepare for your interview
At most agencies, an invitation to be interviewed reflects more than casual interest in a candidate. If you've made it this far, you're at least in the quarterfinals. And if you've done your homework, you should have nothing to worry about.
Before the interview, organize your thinking.
Review your resume and the cover letter you sent to the agency. Decide what key selling points you should communicate about yourself. Think how you can best do this.
Review the information you have about the agency. Be aware of its current campaigns and any fast-breaking developments. Commenting on these can help you to make an immediate connection with the interviewer.
Be ready to discuss your point of view on advertising in general and your area of interest in particular.
Be articulate. Be self-confident and enthusiastic.
But relax and do it naturally. Don't try to recite everything you know. Selectivity shows you are thinking.
Remember, someone is interested enough in your background to invest 30 minutes or more in you.
That person wants you to succeed.