man i rlly cant get the hang of CoD 2's multiplayer. I AM CONFUSED

. MY average lifespan must be like 4 secs. I've been playing the game only like "3 days" bout know but still I have been doing horrible. It's like if i stick my head out of cover a rifle guy will pick me off from where ever, when ever.
and typically i found myself getting killed in like 2 shots with like these smg's taht say they have low dmg. BUt when i am shooting someone, tHEY TAKE LIKE FUCKING 10 shots b4 they go down. and I know I'm not missing cuz i got that hit indicator thing showing up.
whenever i find a target, someone else finds me so b4 i get a kill i get pwned by that guy with the grand from that place i wasnt even looking at.
I need some tips, can plz dont say "just play more" that rly doesnt help
practice on single player, find your best weapon. practice with aiming while strafing. movement is very important. if you find your self getting ambushed and need to run, you need to how to time your jumps exactly so you don't attempt to jump out a window, miss, and get a get a .50 in the back of your head.
personally my best weapon is the springfield. if you can train yourself to be able to match your shots with your scope shake your as deadly as anybody, the bullet always hits were the crosshair is pointing, so unlike games like counter strike, the rifle is just as accurate as it is when your standing in place as it is when your moving, you just have to match it with your scope shake.
another important thing is your weapon selection. usually i go for a sniper and sub machine gun. you can use the sniper for long range and medium targets, and the sub machine gun for close quarters and medium targets. the shotgun imo isn't the best secondary wep to a sniper because the first shot doesn't always kill them, even at close range, and by the time you let off the first round and begin to pump, they will have you on the ground screaming in pain.