When you come across a new business idea, don't limit your thinking to what it is now. Think of it in a more broader sense, i.e. what it could be in future, how it could improve and change. Venture capitalist Fred Wilson wrote how passing on Airbnb was a mistake. "We made the classic mistake that all investors make. We focused too much on what they were doing at the time and not enough on what they could do, would do, and did do."
Here I will try to summarize everything I learned about marketing this year.