Originally Posted by EliteShadowMan
I don't know if theres a specific "good spot" for this achievement. But try to get it early on as i would imagine it's easier.
As for me i did mine on the 2nd Mission "recovery" when i was going for the 2nd secondary mission on that level. Just try to stay in the bushes and foilage and try to take out enemies with headshots, and if they're 2 people next to eachother then kill them in quick succession then it still counts as long as they don't see you.
That's where I did it too. Then I just hit restart if I couldn't get it.