I've spent a lot of years working in marketing agencies and the one thing you learn with that kind of background is how to build relationships quickly. Of course, the thing that's a bit tougher to admit is that some relationships are much better than others. It is simple human nature to say that people work the hardest for someone that they like and respect. This means having an agency and motivating their team to produce their best work for you are not necessarily the same thing. I have written before about some rules for smart agencies to win presentations and provide excellent client service. I take those rules to heart in every one of my client interactions, but recently I also participated in some interesting discussions about what makes an ideal client. As it turns out, there are some very distinct qualities that most folks who work in marketing agencies consider common among their favourite clients. Here are just a few of them with some suggestions about how you might be able to use them to be a better client ... and get better work from your agency as a result.

1. Provide clear direction - This was a clear #1 priority for many agency creative workers in particular who have struggled to interpret vague instructions. Making something "more corporate" in look or language is not clear direction, though you may know what you mean by this. The best clients are the ones who are able to articulate what they are looking for.
2. Invite us to the table early - The earlier we learn about a campaign or new marketing initiative, the smarter recommendations we can bring to you. This may seem in contrast to the first point, as inviting your agency early might also mean you don't yet have clear direction to offer ... but at the early stage it matters less because as long as we have enough information, we can produce the best work. That comes from clear direction, or from early participation.
3. Be honest about success factors - The easy thing to say is that a campaign needs to get X number of views. Many times, the motivation for a campaign are more subtle. The smart agency guys (or gals) understand that part of your motivation is also to look smart in front of your colleagues. That's nothing to be ashamed of - our job is to help you look smart. If we work together, we can all win.
4. Take the advice you are paying for - One of the toughest things to do as your advisors is to tell you when an idea doesn't work. Too many agency people roll over and obey commands, but my experience with clients is that they respect you far more when you have a distinct point of view. The challenge is that once we share it, if you choose not to take the advice, we need to understand why. You don't need to always follow what we say, but the thing we hate most of all is telling you something won't work, being forced to do it anyway, and then getting blamed when it doesn't work.
5. Know what you don't know - We all have limitations in what we know and what we do. The clearest example of this comes when looking at design. If you don't have a design background, you need to tread carefully with design feedback. Take the time to understand why a designer chose to do something a particular way rather than just sharing your personal dislike. A lot of thinking often goes into designs like this, and the most disheartening thing for a creative person is to just be told to arbitrarily change a color or font or image that spent hours to select based on someone else's personal choice.
6. Understand that changes affect timelines - This again is one of the common gripes from people in agencies, that clients change requirements or requests and still expect things to be done within the same amount of time. This isn't reasonable, and the best clients know it. If you need to make a change, its ok - we get it. But work with us to get a real timeline for when we can make the change and get something back to you. We'll respect you for realizing that.
7. Ask our advice - There is a book called The Trusted Advisor which has become the bible for many people who are in service businesses. As the title indicates, the book is about building a relationship of trust that gets to a level where you are considered an advisor even on things outside of your expertise. This remains the ultimate relationship between clients and agencies, and the one we all strive for.