I think the key is to cover everything and break up distinguishing areas of your face, especially the eyes. I also think big lines work better then small ones. For the same reason that Predator/Enigma camo work better than Mossy Oak. If you try to make small details your face will end up looking like a black blob.

This guy has the right idea. But I would have extended the black line between his eyes down one side of the nose, across the mouth, and into the chin area just to break up those facial features even more....