I'm going to go out on a limb and assume you are rolling with a party. Playing by yourself with randoms up against a full team is a bad idea, even if you are a standout player.
In objective modes, know good opening routes on maps and know the "good spawn to have" and try to flip the other team out of it if you don't have it. I recommend trophy systems, very underrated piece of equipment. You don't have to play like a bitch and sit in corners or noobtube, just know lines of sight and communicate with your team to take and defend objectives. Use setups you are comfortable with that can still help you get the job done.
For TDM, it's all about situational awareness. Callouts and lines of sight are essential to map control.
I also recommend running support if you are playing MW3. It's one of those things in this game that if you aren't running it, the other party will. I recommend one guy use hardline with UAV and Counter - just those two. Also, if there is a guy on your team that gets lots of kills quickly, have him run EMP to cockblock the inevitable stealth bombers.