I recommend trying to get this achievement while also going for the Ghost Achievement. This should also coincide with the Poetic Justice achievement and the Just Dark Enough achievement. After each level, the box at the bottom of the Mission Summary screen should be checked where it says that no one was killed. The "Hostiles Killed" and "Civilians Killed" should also read 0 at the Mission Summary screen.
Beware of accidental deaths. This is most likely to occur in Mission 7, where some enemies are near the edges of large heights. Incapacitating them could result in them just falling off and dying, which could void the achievement. A good way to counter this is to pay attention where enemies land, move bodies, and saving often.
During my Ghost/ Clean Hands playthrough, I did not actively look for collectibles and skipped most of the side quests, such as the Granny Rags side missions. The only side missions you should do are ones that are directly involved in using the nonlethal means of eliminating the targets. The fewer interactions you have, the smaller your chances are of having anyone die by your hand.
Since you will not be killing anyone, all targets must be eliminated by indirect (nonlethal) means. All potential lethal interactions should be avoided also. This includes all of the following actions:
The only means of taking out enemies (besides targets) were a standard nonlethal takedown (holding
) and sleep darts from the crossbow.
I did not expect this guide to be this long when I started it, but this should give you a general idea of what is needed for this achievement. If you have any questions regarding this achievement, leave a comment or PM me.