Make a list of 4/5 questions to ask the interviewer about the job. Insight gained from asking these questions early in the interview may help you tailor your responses to better position yourself for the job. Obviously, you can add your own questions. Example:
Why is this job open? What are the responsibilities? To whom does the position report?
What kind of person and what kind of experience would likely succeed at this job?

Make a short list of key accomplishments in your career. Work them into the conversation. Be selective. You want to leave a clear, concise image of yourself.

Make a list of your strengths and weaknesses, and be prepared to discuss them. Make sure weaknesses are not fatal, and are things you are making progress on improving. Examples of strengths are: Your ability to establish a rapport with and motivate your peers and clients (explain how). Your strategic skills. Your ability to get things done, on time and under budget. Best way to do this is by using a mini-case format: situation>planning /lessons learned>strategy>tactics>results. You may want to bring up your strengths at the end of the interview as a way of summarizing what you can bring to this position.

Review your resume, then make a list of anticipated questions from the interviewer’s perspective, especially such items as job moves – why you made them and what you learned. Anticipate questions like: What are your career goals? What’s your interest in this job? Why should we hire you? What’s your favorite ad campaign and why? How will the ad world change in 2/3 years?

Agencies are looking for team players. Talk about your accomplishments, but make sure you also talk about how well you collaborate with your team and others in the agency. Use examples.

Be brief. Limit your answers to 2 minutes unless the situation dictates otherwise. Don’t ramble. You want to come across as someone who thinks clearly and concisely.

Don’t talk negatively about a former agency or boss; it may come back to haunt you. Don’t try to be something you’re not; you may get a job you are ill-equipped to handle. 

Always have your resume in front of you for reference whether it’s a phone or personal interview. Take extra copies of your resume for others you may meet.

Anticipate spending 40% of the time asking questions; 60% selling yourself.

Thank the interviewer for their time and express interest in the job. Ask what next steps are and for a timeframe. Send a “thank you” email within 24 hours to each person you met and personalize each by referring to a particular subject you two discussed. Again, thank them for their time and interest, and express interest in the job.