I guess for me personally it is
1) map knowledge
2)playing the objective
But the most important quality is to be enjoying playing, win or lose. Obviously playing for the win, but also taking advantage of a loss to learn what you did wrong (or what the opponent did right). And knowing when you've had enough when the blood pressure starts rising and the foul language gets loud.
Interesting thread and some thought provoking opinions so far.
Each individual will have things that they are good at, be that cqc rushing or sniping or whatever. But for me the above points are the three things all playstyles need to ultimatly be 'good' at the game and get victories for your team / clan.