Get 4 players together, first and foremost. They do not need to be pros, they just need to know how to shoot, and how to not run into zombies.
Always open the Coffin. Use Bait if you have to for the Zombies (Press LB, select Dynamite, move D-pad to the right once or twice). It gives you more ammo + time. If you run out of time, you will go into sudden death, and unless you are a pro at "circling" Call of Duty: Black Ops style, you will die. Of course, my strategy is for people who are complete noobs at this game, so please, just open all coffins.
The first 11 waves are just surviving and clearing. Stay around the periphery of the map (do not stay near the buildings, go run as far outward as you can). If you are near the buildings, the Zombies will spawn in a circular formation and converge in on you. If you are all spread out around the periphery, then the zombies will have to spread out and look for you. Use the Close Range weapons, and blast them away with the pistols, dynamites, and shotguns.
As soon as the 11th wave starts, spread out. Do not go near your team mates. If one of them is down, leave them (this is not harsh, I will explain why soon). Try to kill as many as you can, and then throw bait when you are being overwhelmed. Follow that quickly by 2 dynamites to cover the entire horde that just ran to the bait (you can throw the bait as far as you want, the zombies will all go there). While you are throwing the bait, and before or during you throwing the dynamite, have another team mate go revive anyone that is down. If you have 3 team mates up, use the 3rd one to help kill / bait the zombies too.
Continue this until you complete the 14th wave, and the achievement will pop.
Congratulations, you won.