MW2 Stradegies, tips, and game play styles?

I want to revolutionize my Modern Warfare 2 play style, so if anyone could help me brainstorm a new way to play and be successful. I dont mind you giving me a detailed description of what you do to be successful or to rack up kills. I want it to be universal in all game modes besides maybe tdm because that is mostly campers and noobs! I usually do some rushing and defensive sneaking around to enemy territory and taking out enemy targets as my friends call them out. This is a good tactic but sometimes I wonder how some players do consistenly good every game and what they do. Plus I want each answer to include a gun they want me to try out and I will post my best game with that gun on here in the extra details! But if you give me a stradegy also include what guns that would work best with and be specific with how it is done and how to practice it. Thanks! I am looking to improve my game and my PSN is: xthemu3lx but dont add me unless you answer with honesty and respect, thanks!