Ask HN: How did you find customers and/or learn sales?

Many advocate that you should already have paying customers before you start building a full-fledged product. Others state that you should have a customer in mind, build the product, release early-and-often and pivot.

Either way, selling and distribution is crucial to your business. I'm curious what approaches people have used that worked for them to find customers and/or learn sales. This part of the business seems foreign many of us that come purely from a technical background.