The easier methods are directly tied to two things - how skilled you are at the game, and how much time you have on your hands.
- Playing on Easy is time consuming, but you'll usually be able to make all of your lives last until you hit 200K points.
-Upping the difficulty raises your score multiplier but you may lose your lives too early.
-Play with friends. The 200K is unlocked when the combined number of points of everyone in the team is 200,000.
-Don't be a hero. Stick to a defensible position near the spawn point/ammo caches. Communicate with your team to eliminate the more difficult units, such as Brute Chieftains or Hunters. The lone wolves die the youngest.
There are multiple websites with people also asking for help on completing the achievements, so you could post your gamertag there if you're low on partners.