This achievement might seem a little vague if just reading the description but it's a lot easier than it sounds. All you need to do is either find a Blood Dragon attacking some enemies or lure one to some, shoot the dragon or get it's attention somehow so that it starts focusing on you, then run and crouch and hide behind something until the dragon loses sight of you and moves on. They have poor eyesight so it isn't hard to hide from them. You can earn this achievement very early on in the game after saving Darling which will be right after you liberate the first Garrison. You can do anytime in the game after that point. There is almost always at least one dragon right by the first Garrison so that is a good area to knock it out. And it won't be hard finding enemies nearby, most likely they will hear and come to you. I posted a video from when I unlocked it. If you only want to see how to unlock this achievement you only need to watch up until 0:56. Everything after that is when I also unlocked the Blood Dragon Down and Just the Tip achievements for killing my first BD and killing one with the bow.