Evan Williams, co-founder of Twitter, put up a list of ten advices + bonus advice for your startup. Please read, understand and conduct.
I particularly think this one is true and should be followed more:
#5: Be User-Centric
User experience is everything. It always has been, but it’s still undervalued and under-invested in. If you don’t know user-centered design, study it. Hire people who know it. Obsess over it. Live and breathe it. Get your whole company on board. Better to iterate a hundred times to get the right feature right than to add a hundred more. The point of Ajax is that it can make a site more responsive, not that it’s sexy. Tags can make things easier to find and classify, but maybe not in your application. The point of an API is so developers can add value for users, not to impress the geeks. Don’t get sidetracked by technologies or the blog-worthiness of your next feature. Always focus on the user and all will be well.