I liked your thread so thats why im gonna tell you something i learned. I have 1.16KDR and 52% Win, so im not the best nor the worse - but my stats would be a lot bigger if i could erase my first month in MW3 (my first CoD online!).
So: a huge advantage is knowing the maps. A lot of people say it, i know, but what i mean is "knowing the maps" had two different steps for me: first, knowing the maps in the general way (knowing places, routes, best paths to go from here to there, camping spots, etc), but the big difference was the second step: looking to the map, looking to your HUD and see the green arrows from your teamates, and, from there, knowing from there which half of the map your team is occupying, and from here guessing where the others are. Knowing it means you can go to places and start shooting your riffle just by guess, even before entering a dangerous spot!
Other thing to me were the Killstreaks: having low killstreaks ready for a bad night that we all have (like Care Package-Predator-Heli), having high killstreaks for when things are going good, and adjusting different Killstreaks to different maps: Reaper for Village, Strafe Run for Intercharge, AH6 for Bootleg (exemple).