The best spots are: At base of beard if he is facing you, butt of wing if he is broadside and the 10 ring if he is facing away from you with his fan out. Personally, my preference is the butt of the wing to keep him from flying off. Best visual reference I can think of for you to look at is the 3D archery targets by McKenzie. The vitals on the targets are pretty close to accurate.

Hope this helps.

Slice