A good way to show respect and keenness is to demonstrate that you know the person you are meeting. Read their profile and look at some of the work they have done recently. Are they an award winner? All of this information will not only serve you better in an interview but will also demonstrate whether there is a clear alignment with you both as people.
In the same way, know the size of the business, have a look at the available listings and understand the target demographic of the company as well as the style of the agency. For example, are they modern and innovative with a focus on social media, or more