JESSICA LIVINGSTON: The most important thing an early-stage startup should know about marketing is rather counterintuitive: that you probably shouldn't be doing anything you'd use the term "marketing" to describe. Sales and marketing are two ends of a continuum. At the sales end your outreach is narrow and deep. At the marketing end it is broad and shallow. And for an early stage startup, narrow and deep is what you want -- not just in the way you appeal to users, but in the type of product you build...