First, craft the Long Bow, which can be crafted after building Jayma's Hut early in the game. Unlike the normal bow, it will kill unarmored enemies in one hit and is also far more accurate on long distances. Once you have the bow, go to an enemy outpost ("Swaras Outpost" to the north-east of your village is recommended). Use the owl to place a waypoint on an idle enemy to view the exact distance. When the waypoint is 70+ feet away, aim a little bit over the enemy's head and shoot the arrow. Note: If you fail, simply let the enemies kill you and you will respawn in front of the camp and can try again.