yes i know becoma a better player but this is unreal, i can shoot a guy with whatever several times and he dont die. i get shot in the foot once and im dead.WTF??  any help would be greatly appreciated.  oh by the way its on MP game not SP

are you wearing body armor?

It's much easier to kill someone from behind, so try to sneak behind someone. If you can't do that, make it at least hard for him to hit you and find some cover, or don't stand still when he's shooting at you. Of course you also want to kill the enemy, to kill someone usually doesn't take many bullets when they hit. That's why you should tap the fire button, when holding it you will spray bullets to all sides except at what you are trying to hit. 3 bullets that hit are better than 30 bullets in the wall behind the enemy.

if u are quite far away from ur target dont aim for the head cos then u will recoil to the head and also it is easier to hit the chest from long range

lmao supersonic  

Fire in bursts.  2-3 bullets at a time.  1/2 sceond pause between bursts.  Don't jump around.  MOVE around.  Pick a good colored crosshair that don't disappear in the clouds/smoke.  /cg_crosshairRGBA "1,1,1,1" is white.  Try diff. valus to get different color combos for your sight.  You got a good connection right?  Pick servers you ping LOWEST to.  Spectate guys who just mow you down time and time again and learn from them.  Optical mouse?  Ya thats a must.  Aim at thier heads unless you got the shottie out, then aim for the lower neck.  Practice, practice practice.  Drink some caffine or some other mind altering substance.  You never know, herb or something might help you play. Don't play INF until you are VERY GOOD.  I just recently started playing it and I am a very good player (with the right ping) and I get bitchslapped around like no tomorrow.  And last HAVE FUN.  If you get mad, stop playing for a bit and have a joint like I do.  

I'd say: skip the cafeine.... drink BEER! After 2 or 3 I play better. I don't think anymore, I just play and have fun. Also, don't be bothered when you get killed: happens a lot. :-)
Try and get to know the different weapons. Some are more accurate, some do more damage. Take notice of the recoil. Pressing the fire button when on fully auto doesn't help. Fire in bursts. Personally I don't like the "burst-mode" of a weapon (takes me out of control). Take your time aiming, then fire some rounds, re-aim, fire again: this should work. If you can't hit him/her, take cover, move to him/her, take out the shotty, and fire away (very hard to miss with a shotty).

*Hips* a bit drunk..

Aaww yes I forgot and you reminded me jonas!!

DON'T SPRAY AND PRAY!!

Yep, indeed: You are allowed to spray and you are allowed to pray, just don't do it at the same time.