The most important thing, the number one lesson we try to teach startups is that the degree to which you're successful approximates the degree to which you build a product that is so good people spontaneously tell their friends about it.
Another thing that startups need to look for is a market that is either started to undergo or is soon going to undergo exponential growth.
Building a great team is the most important thing you do after you've built a product.
A competitive advantage over time is a must-have for startups.