What does it take?
FAMAS!
And playing blue on each map helps (map designers hate red). Seriously, its all about being mobile when you need to be mobile, and awaiting the enemy when you know he is likely around the corner. Predicting what the enemy is likely to do, or where he is likely to be goes a long way to running all over a map casually slaughtering as you go. How does the sniper seem to headshot you time and time again? Its because you keep sticking your head in the same place. How come you are able to turn a corner and waste a bunch of enemies? Cause they were running to battle, making lots of noise, and not expecting you. In other words, it takes smarts and practise (skillz).