There are lots of great answers in this thread and I don't disagree with any of the longer ones. (We also can show counterexamples to the short numeric list.)
There is a
great answer on the importance of mentors in another current thread that I'll link to. Your team doesn't need all of these, but having many of these elements is key.
I'll add two other elements that I think are key:
1) Play for the entire game, and think strategically. It's not having the best robot, the best driver, the best scouting system, or the most resources. It's coming up with an effective combination with strategic consideration. Mike Corsetto has a great presentation on this as well as Karthik. And this requires pre-thought; it doesn't start on Kickoff.
2) Constantly work on improving your robot. Look at pictures of 2013 robot at Central Valley vs at Champs. You won't recognize it. 1671 started improving their robot all through competition this year, and they were the shock pick of Champs.
3) Take advantage of the good luck you're handed. 2014 was the year we relied on the least amount of luck, but 610 having one really bad match poorly timed for 1114 made the difference for us. In 2013 we used other teams' unfamiliarity with us to our advantage to exploit a favorable schedule. This year we drew three teams that we were already very familiar with in our division and were able to put them together into an alliance.
I know that I'm not alone in making this offer as Mike, Karthik, Jared and Suri have posted here: please feel free to message me about any advice or resources we might be able to provide to make you a more successful team.