Note: This achievement must be done on Normal
This achievement is really easy. You can do it on any mission, but try to do it on the first mission so you can get it out of the way. The main thing is to stay back and NOT rush. If you are getting injured and are about to die (you screen goes black and white with red around it) stay low behind cover and wait until you heal. But try not to get that injured in the first place. Just stay behind cover for most of the level and use your Assault Rifle or Sniper Rifle. Try to avoid hiding behind cars because they can blow up. If you must hide behind them, make sure they are not on fire. The missions are relatively short so you should have no problem with this.
**See Sergeant Major for tips**