So, you're a noob. If you aren't a noob, you're a good player that's looking to maybe get a little bit of an edge in Black Ops 2. Whatever the reason is, you're likely here because you want to play better at the game. I'm here to suggest some things that ought to help you improve your game dramatically within a short amount of time. The list of these tips aren't in order of importance, so don't worry about that.
1.) Play with friends and communicate. This one should be an absolute no-brainer. If you're just going out and playing any game mode other than a Party Game or Free-for-All by yourself, you're likely to lose many games and end up frustrated. If you want to see your win/loss ratio climb (and even your K/D can if you have a communicative team), then you'd better get a group of at least 4 people in each match you play. I understand that most game modes are 6v6, but a group of 4 and 2 randoms will beat a group of 6 randoms just about any time.
2.) Use smaller Scorestreaks. What I mean by this is, don't bother trying to get the K9 Unit or the Swarm ... chances are that you'll never get those once. Instead, use things like the UAV/Hunter Killer/CUAV/Care Package/Lightning Strike. My personal combination tends to be UAV/Hunter Killer/Lightning Strike because I find it most effective overall, but to each their own. These Scorestreaks are easily attainable in any game mode -- assuming you go for the objective -- and you'll have a streak almost at all times.
3.) Use guns appropriate to the map. With these Black Ops 2 disc maps being as small as they are, an SMG will be perfect on nearly every map... even a shot gun can be super effective on a number of them. On maps with some longer sight lines (and there aren't many of them), and assault rifle will work a bit better. Overall though, an SMG is probably the type of gun to use right now in Black Ops 2 until Treyarch either nerfs them a tad, or releases larger maps as DLC.
4.) Don't use random perks. If you're playing most objective game modes, you're going to want to play smart. I personally love to run a class that has Ghost AND Flak Jacket in the first slot, Cold Blooded in the second slot just because, and then Tactical Mask in third. These perks (especially Ghost, Flak Jacket, and Tactical Mask) work wonders in objective matches for too many reasons to count. Ghost allows you to flank (Don't stop moving with Ghost, otherwise you'll show up on the radar), Flak Jacket will take the brunt of explosives, and Tactical Mask renders all tactical grenades other than EMPs useless. In game modes like Headquarters and Hardpoint, I feel like those perks are essential.
5.) Likewise, don't use random equipment. And to add to that, don't bother wasting a Pick 10 slot on a grenade if you never toss them. Like the perks I listed above, I find that things like Shock Charges and Bouncing Betties work fantastically when defending objectives. If you don't get a kill, you at least get a hit marker that'll let you know where to look and possibly get the kill.
6.) Switch button layout to Tactical. I decided to do this soon after starting to play Black Ops 2, and I haven't looked back. What this does is switch the "panic knife" button with the crouch button, making it easier to drop shot. Drop shotting tends to be useful when someone unexpectedly comes around the corner, or when you're getting shot in the back and need to duck down quickly. Many people consider(ed) this a "douchebag" tactic (including me), but I decided, if you can't beat them, join them. I don't drop shot too often, but it seems to work a good bit when I do decide to do it.
7.) Learn the maps. Another basic strategy. Running around on Hijacked with a sniper is a terrible idea ... for the most part. I've seen people do it and get a good K/D, but a K/D doesn't mean a thing in an objective mode. If I die from a sniper in this game, I tend to feel pretty good about my chances for winning, since that player is way more than likely not helping his team. Also, you'll want to learn key choke points, and also some nooks and crannies to "camp" in when an objective is nearby. You should definitely look around for headglitching locations. It shouldn't be too difficult -- Treyarch has seemingly put them everywhere on just about every map.
8.) Try League Play. It's there for a reason. Whether you consider yourself a "serious" Black Ops 2 player or someone that plays pretty much exclusively for shiggles, League Play is there for you. Granted most people playing it will be playing to win, you'll be paired up with people of similar skill levels, so you don't have to worry about getting "pubstomped" when playing in random matches.
9.) Finally, experiment with classes. Don't bother asking what a friend uses as his primary, secondary, equipment, or anything else ... he/she may not have the same play style as you do. So rather than do that, mix and match with the Pick Ten and figure out what guns/perks/equipment suits you.
These 9 ways to improve in Black Ops 2 are just a few of many. If you want to ask for more tips or maybe want to play Black Ops 2 with me, send me a message on Xbox LIVE (OrdealByFire). My friend list will be full, so yeah. Send a message first.