Hi guys how's it going?

I've been playing the Xbox 360 version of CoD: WaW a lot lately. This is the first Call of Duty game I've played, and the first time I've
EVER played a first person shooter online(GoW doesn't count). It's a good game and I'm currently at Lvl 34. I've gotten a few nice machines guns and sub-machine guns. These are my favorite type of weapons. Some are better than others...I usually like to use the M1A1 Thompson, Type 100 or the MP40 Sub machine gun.
The problem is, I am having a bitch of a time getting good at aiming. I am constantly losing gun battles because of my poor aiming skills. When I am near or approach an enemy, I have a hard time getting my cursor focused on him long enough to get a kill. Most of my kills seem to be by luck, as I frantically move the analog knob back and forth hoping and praying my gunfire makes contact. I don't know, maybe I haven't been playing first person shooters long enough using an analog stick, or maybe my sensitivity setting is wrong? Right now it's set at medium. Should I alter it?
What else can I do to improve my aiming skills? Is it something that improves over time and just comes naturally? Is there a perk in the game that makes aiming the cursor more steady when aiming in using the left trigger? I already have the "steady aim" perk but that is just for when you shoot from the hip.
BTW my little cousin is only 15 years old and he's a
GOD at this game, averaging 25 kills in team deathmatch, sometimes as high as 35!!! I'm more than
twice his age and I suck. WTF is up with that?

: