Another way I've improved my game drastically is not to leg it around everywhere. I've said before I hate camping, but sprinting around on this game makes you an easy target as you can run past someone, they shoot at you and then you run into someone else (meanwhile everyone now sees your dot on the radar because you're shooting, so they home in on you).
I've found I don't run much now, maybe stay by a window for a little bit, before creeping around corners etc. I think my UAV jammer seems to work, not sure entirely though. But creeping around is much better for me, maybe because I'm more suited to a R6 style of play than Halo.