First, you need the "Ambush" stealth skill. You can buy skills by going to the mirror area and sitting in the chair (mirrors are found at every safehouse). Then, lean at a corner and when an enemy approaches, perform a corner takedown to get the "Wait For It..." achievement. This can be done anywhere in the game. You can lure enemies to you by popping out of cover for a moment and letting them investigate the area. However, be careful they do not become fully aware of you, as the corner takedown only works while you are in stealth.