This should be self explanatory, but if not, you can get this very early in a game. I chose Thane as my character, and went looking for some prey. Find an AI within one or two turns and attack them, chances are that you'll defeat them and earn the achievement.
Just some extra info, you start out at the bottom center position, I headed up and anti-clockwise and found the rat with a turn, he was easy pickings so early on. Just do not equip any of your cards until after this battle is over.