This achievement should come naturally if you approach the levels stealthily. I would really recommend to try this on human enemies. Use trowing knifes to silently take out enemies so that they won't shoot at you, guaranteeing that you won't take damage.
A good early level to try this on is LOST TUNNELS in chapter two. This is where you meet the bandits. Other levels that are good places to try are FRONT LINE and BLACK STATION.
You can also cheese this achievement by stealthily killing one or two enemies right after you got a checkpoint and then reloading it. The counter only resets if you get spotted and not when you reload checkpoint.