1) Hire your marketing agency
Before you waste any agency's time, be sure you have the support of your CEO and the board of directors. I can't tell you how many reviews wind up at a dead-end because senior management didn't bless them. Once you have the green light, don't bother sending out RFQs, which precede RFPs. It's a waste of the agency's time and your own. Research what kind of agency will help you succeed. Ask the trade press and marketers who do great work for agency references. Narrow down a small list. Check their websites and their past work. Then invite three or four shops in for a chat. You (the client) do the talking. Tell the agencies why they should pitch you. Let them ask you questions. (It's a briefing session and a vetting session in one!) Next, invite yourself on a visit to each shop, get a sense of the culture, and end on a lunch with whoever can attend from the agency. This phase serves to test chemistry and compatibility. You'll know at this stage whether to do business with an agency. Finally, end the review with a pitch, where each shop struts its strategic stuff -- but not creative. I repeat: Do not request spec creative. Asking for unpaid work is disrespectful to agencies.
2) Get great work from your agency
Give your agency full access to all relevant parts of your company, including key management. Tell them you believe in them. (Agencies are sensitive creatures.) Tell them what you expect from them. Respect the creative brief. Give your shop a generous budget to work with. If not, a sufficient one will do. But be warned: This is no place to cut costs. If you expect great results, put your money where your expectations are. Then leave your agency team alone and let them do their thing.
3) Compensate your agency
Don't play 20 Questions. Be honest. You know your budget. Pay them fairly and you're likely to get more than you asked for in return. And pay on time.
4) Motivate your agency
If they are busting their humps on your behalf, recognize them. A few positive words go a long way. If your company sells a product that most people need or want, send your team free product(s) regularly. Courtside seats aren't bad, either.
5) Fire your agency
All relationships begin with champagne and end in tears. That life cycle can take months, even decades. But it will come. And when it does, be the first to tell your agency what you're thinking. There's nothing worse for an agency than seeing itself axed in the trades, or hearing it through the industry rumor mill. I truly believe disrespectful clients get their comeuppance.