I was where you are.
It's exactly like a baby learning to walk. The real only prescription for learning to walk is to walk, then walk some more.
Here's the real problem which is arrived at in all sports: We think with our fontal lobes, but we do all our sports activity with our cerebellum, the most primitive portion of the brain. So, people can attempt to describe how to accomplish a phyical activity, and a person can be open to "understanding" that knowledge. But, it is the imputing of that to the cerebellum which is important.
So, even though the first arrow is important, while practicing, they're all imporant (and equally unimportant). What I mean is to take yourself just about as seriouly as a baby learning to walk. You will notice that babies don't beat themselves up when they go "plop." They laugh and get back up and go some more.
I've been in the basement shooting arrows late at night when my arms were so tired I couldn't draw properly. Perhaps I shouldn't do that; maybe I'll develop bad habits. But, I don't think so. I think that shooting 10,000 arrows will lead to some good things. And, that has pretty much proven to be the case.
G. Fred Asbell has been most helpful to me in this. It seems with him that it's a "ying and yang" sort of thing - don't always get so serious about little details - instead just enjoy the shooting. I note that Fred reports shooting hundreds of arrows per day, however.
So, if one arrow goes low, don't adjust up. Instead, forget about the low arrow and shoot another where you know you should. After a while, you will nail that first arrow more often than the following arrows because you have more focus on the first arrow.
Hope this helps. Hope you enjoy your shooting.