This is the simplest way to get this achievement and the story mission basically hands you the achievement.
This is best obtained on Sequence 2 mission "A Faithful Acolyte".
After you kill the alligator you will have to kill a whole encampment of enemies. Simply go in poison the guy watching from a post to the right then jump down. Alert the enemies and when they come in close drop a smoke bomb and use the Sugarcane Machete to kill them one by one.
Also if you hit the first guy with the poison dart while in Eagle Vision you will unlock the "Predator" achievement.