Review this thread that I have posted on a few times:
http://www.codforums.com/threads/black-ops-2-what-is-your-opinion.2385/
I give out some tips on what made me a better BO2 player. When I started BO2, I sucked pretty bad too. It tripped me out because I've played COD since the first Black Ops. I was a 1.87 when I started the first BO and then when MW3 came out, I was a lot better, 2.13. Now in this game, nothing seemed to really work. Then I started to really think of how the maps and game is designed, then I built my class around that. I used to only use assault riffles, but in this game I have resorted to SMGs. A lot of the maps are a lot smaller in this game so it appeals to the run and gunner.
Try out the PDW, I love this SMG. It comes with a 50 round clip.
Further, I like to sneak around the edges of the map, so I use Ghost and a silencer on my weapon. My class is setup like the following:
Primary Weapon:
PDW - (Silencer and Laser Sight to be silent and improved hip fire)
Secondary Weapon:
B23R (No attachments)
Perks:
Ghost and Hardline (Stay invisible and I like to go for the higher kill streaks and hardline takes 20% off)
Toughness (I say this is a must, a lot of gun battles are up close and you don't want to jump around alot)
Engineer (Nothing worse than running around and getting killed by a dang bouncing betty)
Lethal:
Bouncing Betty (These are awesome, especially if there is a camper sniper in a window. Just throw it in and watch it work) You can also use a C4 here too.
Tactical:
Nothing.
As for score streaks, I like to use Stealth Chopper, VSAT, and Escort Drone. If you can get the Stealth Chopper, you should have no problem getting the other two. These three build on themselfs really nice. Drop the Stealth Copper on one side of the map and run around the other side of the map with the escort drone above you. It's great because every chopper kill is 25 points and the VSAT assists are 10 points (until you die). If you're killing people consistently while they are up, then it's really easy to get the three score streaks again.
This is a run and gun class, but has really made me enjoy the game a lot. I'm not a sniper/shotgunner, just seems cheap to me. I like a challenge when I play and using those don't give me a challenge, it's to easy. Oh same goes for target finder, blah so g@y.
Also, switching to a pistol when you're out of ammo and in a gun fight is WAY faster than even attempting to reload. Try to switch to the B23R instead of reload and fire off a few rounds to get that extra kill instead of dying when reloading.
Lower your sensitivity down. a notch or two. Once you get a good feel for it, gradually increase it.
Lastly, in my opinion, knifing is a joke. I have switched the knife button with the drop button. I don't drop shot to much, but it's way better than missing a knife and getting killed. I just shoot from the hip rather than knifing and it works out a lot better in my opinion.