Serial entrepreneur and investor Steve Blank teaches a class on entrepreneurship on entrepreneurship at UC Berkeley, Stanford, and Columbia, as part of the National Science Foundation Innovation Corps. Whether you're a first-time founder or an established CEO, there's plenty that you, too, can learn from the lessons he gives his students.

In an Inc. Playbook video, Blank reiterated a critical piece of advice that he often gives in his class when it comes to planning a startup: "Get out of the building."

Blank explains that entrepreneurs fail when they try to sell their products before actually learning who their customers are. "Customer discovery is not sales," he says. "Customer discovery is a lot of listening, and not a lot of talking."

Meeting those initial customers shouldn't be difficult, particularly in the era of Facebook, LinkedIn, and Twitter. The key, Blank says, is to then have them connect you with other customers, thus creating a "sum of data points over time" from which you can develop your business.

He added that it's always good to end conversations with this query: "What should I have really asked you?" The answers can take you in an unexpected (but ultimately fruitful) direction, provided you're willing to listen.

For more on customer discovery and the value of getting your hands dirty, check out the Playbook episode below.