The easiest way to get this achievement is on "Diamond Store", as there are always 4 guards and the routine to stealth it is pretty easy!
Just don't forget to kill all the 4 guards with shurikens. If you manage to kill them within 90 seconds, you'll also be rewarded with this achievement:
Here is a video from GeneralMcBadass to show you the easiest way to stealth this map :