From everything I've read, instinctive shooting requires a level of focus that is hard for the average human being to maintain. Which is used as an "excuse" as to why we don't do as well in tournaments as sight shooters. Well, no one likes to make excuses, but it would be interesting to see how an excellent instinctive shooter and an excellent sight shooter would compare on a roving course where each got only one shot at each target, and all targets were at unknown distances from 10-40 yards.
But the gist seems to be that if you want to maintain a high level of focus, then the best way to do that is to fire only one arrow, retreive that, and then fire another one from a different location.
Personally, I don't like to do that, because it's too much walking and too little shooting, so I just concentrate my focus, pitiful though it may be, the best I can.
Sometimes it's interesting to reverse the question. I usually shoot a few arrows in my backyard in the afternoon after I come home from work. Sometimes they group, and sometimes they don't. When they aren't grouping, I can usually identify some source of stress that is preventing me from focusing. Sometimes the source of the stress isn't on the top of my mind, and my arrows spreading all over the target serve as a visual indication to me that I may be burying some issue that needs to be addressed.