For the Ward!

Just completed this as Horde, to do it you need to kite one of the trolls just east of the Dawnseeker Promontory. There is a group of trolls, Since one of them is named, I would assume that he is most likely there as an eventual end-daily kill target.

There is a small Devilsaur in the group, which will also count towards the achievement.

As mentioned by some people, simply bring an enemy down to ~10% HP then let the Ward finish them off.

For anyone trying to do this achievement in the first days of the patch, you cannot complete this until you have progressed in to the further stages of the island.

For Alliance, I kited over an Animated Warrior from the center, one that was as close to a ward as possible, just simply walked backwards with it and attacked it lightly as possible because the kite distance isn't exactly short. Even so, it worked on the first attempt. Hope this helps!

Edit: This method will work for any Alliance who have access to the Kirin'Tor Wards.