Just some thoughts straight off the bat. Have clear defined objectives and measurement. It will keep you and the agency (for want of a better term) accountable. Begin building out a brief. Background, objectives, unique value prop for your business, lessons learned from previous efforts, current channel presence, best practice examples if they exist etc. Basically crystallise all the different conversations you’re having into a simple document. Then go hunting for people who can help. Look at forums, industry websites, LinkedIn, reach out to your network, find competitors who are doing good stuff and do some research on who they used. Fine examples of smart work from outside of your own industry too. Then I have a conversation with my "long list" to get their vibe. Do we gel? Do they have insights that suggest they know this stuff better than me? Remember, you’re paying them because they’re smarter than you at this stuff. Then cull your list to a short list. Take a look at your brief based on the conversations you’ve had then refine it. Then fire it off for a "reverse brief" of sorts where they put their thinking down on to paper. Whether it’s a full agency or a single consultant, you all need to have documentation to cover off what their understanding is of your brief. Without it you have no leverage to review their performance or means by which to keep them accountable. If they don’t sent to run through that then they aren’t the right fit. I’ve used this broad approach for projects big and small and it’s always served me pretty well. Marketing is a pretty organic process but you do need something to reference as you plot ahead. And never forget that vibe or gut feeling or whatever you want to call it is a big consideration. I’ve taken agencies off $5m+ projects because they were hard to deal with in that initial phone conversation stage. Likewise I’ve put small guys through to short-list because we had a great connection and they seemed to just "get it."