Small-Business Marketing: Where to Start?

How should small businesses approach planning a new marketing venture? What's the absolute first question they should ask themselves when starting out? What's the one piece of information that will guide and shape the rest of their planning and make all the other details fall into place?

I ask because I had an interesting conversation this weekend with an acquaintance who is struggling with his own marketing. A salesman in his mid-30s , this acquaintance has doubled his sales for the last three years but knows that kind of growth can't happen forever without devoting some more serious attention to marketing. A loosely independent salesperson with no support staff or resources outside himself, he has to plan, budget and execute any and all marketing on his own, which was his whole problem.