First of, i'd like to say, play with a team. Playing with a team, preferably people you know makes this game much, much more fun, and you level up faster, win more, and die less (You die from some kid behind you a LOT less). Play to win against other teams. Sacrifice K/D for the objective in team vs team. Farm k/d against randoms to make up for it. But play smart. And don't ragequit. Eventually you'll love tougher games where you struggle to pull a 1 k/d against a good opponent.

And, don't get mad. It makes you worse, and it makes your teammates think its ok to whine when they get noobtoobed, quickscoped, spawned on, etc. Gay stuff happens all the time in this game. Deal with it.

Also, this is a lot of info i've read here, and on other mw fansites, and ingame experience.

Buy a headset if you can. 30-60$ for a decent wired one. They help. Also, get a good internet connection if possible.

GAMETYPES
Play gametypes you like. KC is the fastest because you get both score and kills, and more kills = more challenges. But i enjoy domination and sabotage much more, as spawns are more consistent. Play what your team is happy with.


TOKENS
Secondly, tokens. IMO, using 10 tokens in theory saves you only ~10 hours to tenth. I used 1 on dblxp total, and I regret it. First, unlock a gun or 2 that you love. I chose the mk14 and the mp7, both are unlocked late, and are some of my favorite.

The rest of your tokens i would use on custom classes. The only USEFUL thing you keep at 10th. I bought the last title/em package, and never use them. They, IMO, are a waste.


TACTICS
My main tip, besides a team, is play the maps you like. As a team, you can back out, and rejoin infinite times you chose a map you want. As long as you have a large team (4-6) you won't merge 99.9% of the time.


COMMUNICATION
Map control and communication are also key. Know your teammates, know how they play. In dom, i play with the same 4-8 people, we all know where to go and what to do to secure the middle and the spawn with an advantage, and execute this quite well.


SPAWNS
Learn spawns. Seriously, i don't think i need to explain this. Knowing the spawns is the difference between a multikill and a death from behind. And chances are, when you kill someone they will spawn behind you. Turn around, or use a motion sensor to watch for group spawns. Also, in dom, if you run into the enemy point, and kill all the enemies, 90% of the time they will spawn at your point. Tell your team when you do this so they don't get killed from behind.

I'll update this with dom spawns if people are interested.


CAMPING
Camp. And no, I don't mean in a corner. Use cover near a broad line of sight. Sacrifice cover for volume of enemies though. Seeing 10 people and killing 7 of them > seeing 3 and killing all of them. If you aren't getting enough kills where you are, move up.
To get the most kills and points, you must see the most enemies. Be in the center of the map, be near enemy spawns, and be behind cover. Behind behind cover = instant win of 90% of your gunfights. Plus, once you kill someone, they will generally run back for revenge. Free kills.
I've also found that "camping" improves my aim, so I win more gunfights when i push / rush.

Pushing spawns (ie, rushing in gametypes like dom) results in 1 player with a ton of kills, the rest with unnecessary deaths from behind, unless your team communicates quite well. The few maps my team does this on are Bakaara and Carbon, as spawns fluctuate a ton, and you can easily pull 4k+ points in a game of dom pushing hard. Hardhat too, in non competitive gameplay.


KILL CONFIRMED
Run with 2-4 people. 6, and your spm suffers. Run as a group to get denies, and share tags/kills, or run in pairs, both work well. Get your own tags asap. Many guides on this, so i don't need to go in depth.

CHALLENGES
Challenges are key, there are so, so many different ways to earn 10k challenges. The only thing i don't change is the proficiencies one. Kick or attachments are usually my prof of choice.



I'm only going off of the top of my head, so here are a few tips:

-Hardline + specialist. Always hardline. Always. Throw flashbangs and stuns everywhere for free assists and specialist bonuses.
-Switch up specialist ks every 150 earned. I'll usually go assassin, marksman, quickdraw. When i get 150 assassin, ill swap it for marksman, quickdraw, steady aim. Moving forward.
NOTE: marksman and assassin i usually max out, both i find quite useful and don't rotate them out that often.
-Switch up guns every 300 or 500 kills.
-Get level 10 with every machine pistol every prestige. They are all quite good.
-Jump in the well on seatown every prestige.
-Blast shield is a very easy 30k exp, as are quickdraw, assassin, hardline, soh, scav, recon, marksman (hold the left stick with ANY gun without the breath perk to unlock), and all of the 3rd perks minus sitrep (harder to do legit, you can knife your trophy if you really want to get eq kills).
<<NOTE: WILL LIST EASY CHALLENGES IF PEOPLE WANT>>
-Focus on perk and specialist challenges. Seriously, they are easy to do and give a ton of exp.


DOUBLE EXP
Like i said before, double exp is more like 1.4x, at a max. It doesn't double specialist points, challenges, or match bonus, which make up a HUGE portion of your double exp.

Challenges are FTW. Don't feel like i can say this enough.


GUNS
Use multipurpose guns (meaning, all attachments work well), and do attachment challenges. Guns i commonly use are:
m4 / g36c / acr
mk14 / t95
mp7
pp90 / p90
l86 / pkp / mk46

Don't snipe or grind shotguns if you're powerleveling. If you're pulling a ton of kills with either of these, chances are you DON'T need this guide.

STALKER

Use stalker on all guns, except for maybe subs. Being pre-ADS in a gunfight > everything. It may take some getting used to (aim wise) but it makes a huge difference to be ADS before an opponent and also be able to strafe them. Plus you don't die to betties.

LMGs

LMGs are some of the MOST underused guns. But they are quite good in the right hands. Given the mobility issue stalker works amazing, allowing you to win some head to head gunfights. But LMGs do best in high volume situations where the enemy isn't immediately shooting at you. Because of this, i've found silencer + kick or extended mags to work well on all (most, imo the l86, pkp, and mk46 are the "better" LMGs) because you stay off the radar.
Thermal works well also, but given the mass amount of assassin users, i don't use it often.
LMGs work well with tac insertions to stay in the action when you die, or with a portable radar to watch your back. Be in the center of the map, or near a choke point.
Preferably be able to prone as you have almost no recoil when doing so.
I've also found that when playing with a team, em+impact+recon pro works well in combination with UAV. For example, on lockdown, i'll spray into the middle building and hit a few people, reconing them, so that i or my teammates can get an easy kill.
Try to use LMGs on gametypes where a defender role is needed, rather than, say a TDM game.
As for a setup, i'll usually run something like this on a map like mission, hardhat, dome, village.

L86 Silencer/kick
Recon / Scav if going for an MOAB
Hardline
Stalker
Specialist (marksman, recon, assassin)


POINTS PER KILL
300 kills for a gun is ~17.5k xp.
That means you, from just using a new gun every 300 kills, get ~105 exp total a kill in KC.
This isn't even counting proficiency, gametype, equipment, headshot, perk, strike package, and other challenges. A single kill could count for 6 different challenges at once.
Managing challenges well, along with tags can get net you anywhere from 150 to 500 exp per kill.

BOOSTING / GLITCHING
Don't do it. Period.
If you're going to do it for whatever reason, don't use your main account.
Boost to 10th on a throw away, or whatever prestige you want. Boosting a prestige or 2, after getting a legit 5th, then getting it reset is dumb. Boost smart, or don't boost.
Same with glitching. Not worth the risk IMO, but its your choice. Play for fun.

Worth the read if you're trying to prestige fast. Will update if this gets a decent amount of replies / views and will make it easier to read if the above happens.

Note: I am 10th 80 with ~8 days of play, took 6 to hit 10th, a 3 wl, and a 2.2 k/d. I'm not amazing, but i play with great people, and feel like most of this info is good and accurate.
Updated 1/1/2012