Max Payne 3

I'm always hesitant to write up a solution as I'm aware it won't work for everyone and I feel it has to be flawless or it wasn't worth my time (and wasted the viewers' time), but I'll give it a go since it came easy to me and I see less than 20% of scanned gamers have it.

Start up a Rookie Deathmatch game, with, and this is key, Free Aim, as opposed to Soft Aim. Less people play in Free Aim, firstly, so I found most matches started with 3 or 4 folks, with some joining up later but after you've built up a score that those latecomers won't be able to catch. Plus, it's harder for players to get a bead on you since the reticle doesn't stick. The map I won it on (and the most popular deathmatch map from what I can tell) is the office building one (can't find the name of it anywhere online at the moment); the one with all the cubicles and the open lobby with stairways on each side. I'd recommend the first custom class with the AK47 as it is a fantastic free aim weapon. Something key to remember at all times is the melee (Y button) which prompts on the screen when you are close enough to perform. I get the idea many players haven't yet found this out (especially this being for rookies) because it has seldom been used on me yet highly utilized by me and really, the key to my success thus far, as it is a one-hit kill. Be warned it does take stamina to melle, so if you've been sprinting or rolling around and come upon an enemy don't be suprised if your melee doesn't work. Just back away from the player and fire from the hip. Firing from the hip is also key when running down a fleeing enemy, and the AK works wonders with it. Just always be aware of the red dots on the minimap and the noises of combat going on and above all, don't be afraid to die. Use discretion to some extent, but this being a free for all, just go out there guns blazing and meleeing.
I consider myself an average competitive MP player (average 1.3 or so k/d ratio across all games), no superman by any means, but using this gameplan, I won 3 deathmatches in a row with two of them by more than 5 kills. If I can do it, I know you guys can. Go out there and get it!

Deathmatch is an all against all game-mode you basically have to get the highest kill rate out of everyone in the match being killed yourself doesn't lose your score, this can be done with 2 people in the match but be warned that randoms can join during the match which will mean that you will have more people to kill and your win percentage will go down with practice and luck you will get it.

If you can use custom class to make yourself lighter to make you heal and move faster also using loot can be your friend for painkillers and adreniene.

(hope this helps - please comment if you vote negative).