Your class is important and this could be whats wrong and these are just some suggestions for your classes:
Shake things up a bit, don't use the same ol' every game if its not working and I don't just mean change your primary weapon I mean change EVERYTHING, who knows something you may have never tried could be the key to changing everything...

Class tips - Sub machine guns, you want to be using something accurate that YOU can control for example the Vector has very little recoil and a good fire so you can win gunfights easily at medium and short range also if you find yourself spraying allot with other guns such as the scorpion or MSMC then choose a decent secondary weapon. The B23R we all know its overpowered so why not use it? Or even the KAP-40 isn't to bad but I would use extended mags as the fire rate is too quick for the clip size.
I would recommend the M8A1 or the Type-25 as the best assault rifle but others disagree, some say the Scar H and others say the MTAR because of its accuracy however all 4 of these guns are perfect for the bigger maps such as Turbine.
Shotguns, please don't use these but if I have to recommend one is has to be the Remington obviously, ahh jesus that guns ruins me.
If your a guy who likes to snipe but is having no luck, I would say try either the DSR or the XPR as these 2 are by far the best 2 snipers and the attachments for these should be the laser sight and Ballistic cpu.
I'm not too familiar with the LMG's but I've heard that the MK48 with Target finder and grip is perfect.

Perks
Ghost in this game is key as the UAV spam is ridiculous and you don't want to be constantly saying "How did he know I was there!" so use ghost also if you're an objective player flak jacket is key and this may seem like simple tips but they could just save your life one kill away from that swarm.
Toughness is often overlooked but is very useful especially if you're fed up with losing gun fights as even if you're being shot at you can still kill them as you haven' flinched a bit! Honestly give it a go. Personally believe that from the tier 2 perks scavenger is the only other useful perk because not only does this refill ammo but also C4.
Dexterity is fantastic! To be able to be sprinting and then be able to look straight up and instantly have your gun aimed in at the enemy is so helpful its unreal, this will help you win the majority of fair gun battles because you have the advantage by far. Tactical mas has to be my favorite perk 3 by far because in this Flashes and shock charges are overpowered too far and I couldn't stand them anymore but with Tac mask you're immune to them so its perfect.
However these are only my tips but don't be afraid to try other perks! Surely its worth a
try?

DO NOT RUSH THE SPAWNS, in BO2 this doesn't work (unfortuantly) for a few reason, 1 being that once your hurt and faced against someone with full health or more than 1 person you will definitely die so don't try this also once they spawn again you will only be annoyed that got killed by like 5 enemies however if you are going to do this you will want an organised team.
Be smart. If you're hurt, hide, if you play behind enemy lines use a silencer then you can take them all out easily and if you don't have a sniper knife at least one of them but don't chase them.
I hate to say this but... Head glitch, why not? Everyone does it so there's no reason us pro's cant haha, its an easy way to pick up a couple of kills.
If you're going to camp (don't be afraid to) then don't stay in the same position, try to dominate one area and pick the enemy off one by one.
Stay near SOME teammates then you know if one of them dies you can get the enemy that killed them however this doesn't work for everyone and if you're a lone wolf then I recommend using UAV.
The key to succeeding in this game is to not be stupid.

Can't reach the high ones? No worries, here's a set up for you:
UAV, CUAV, Guardian. or. Hunter Killer, CUAV, Hellstorm missle. Or. Hellstorm, Lightning strike, Sentry gun.

Now here's for the average player:
Lightning strike, Stealth chopper, Escort drone. Or. Hellstrom, Lightning, Stealth chopper. Or. Dragon fire, AGR, Stealth Chopper.

Above average:
Stealth chopper, VSAT, Lodestar. Or. VSAT, EMP, Dogs. Or. VSAT, Lodestar dogs/swarm.

Score machines streaks - UAV, CUAV, Guardian/VSAT

However there are many combinations and these are only a few so just try out anything, even if you think its crazy!

I would say that the best ones have to be -
Laser sight, EO tech Sight, Foregrip (SMG's) and Silencer
because each of these play a key part in winning those gunfighs especially the laser sight and the silencer just helps that extra bit to keep you alive by staying of the radar also EO Tech sight to me seems to be the most accurate and nicest looking sight but its also personal preference.

The BIGGEST problems with BO2 is undoubtedly the lag. So here's a few way to fix it:
1. The most obvious thing that everyone knows is to set there search preferences to 'Best' but another couple of ways to fix this shocking lag is too
2. use a wired connection and plug the cable into the bottom port of your internet router (Not too sure what its called) and when doing this stand your xbox up, I don't why this makes a difference but for some people it does.
3. If you have to be wireless then make sure your wireless thingy is on top of the xbox or as far out in the open as possible.
4. BO2 requires as much connection as possible so if your sister is on the laptop or computer anything that links to your internet just turn it off, try to make sure that the only thing connecting to the internet is your xbox.
5. If you're with virgin media then ring them about doubling your speeds if its ready in your area, this is completely free and you are entitled to it and this could just stop the lag.
6. Ring your service provider and try to resolve the problem that way, however they aren't usually too helpful.
7. Simple move your xbox to somewhere else even if that means just moving it 2 feet, honestly just try this.
8. Try this - [ Register or Signin to view external links. ]