different for each player
That is something that I don't completely buy.
I think that it is our tinkering nature that keeps us from really getting better.
I know that all of my tinkering has prevented me from improving. TGM wasn't any help because when you first start to learn this 'stuff' you are given so many pathways to go that it is imposible not to play around for a month, or in my case 2 years with all of the new concepts.
This won't be the case for everybody. I've coached college players; they all needed to work on their short game of course, but a couple of them needed to make their first priority their golf swing. There are a couple of "short game tests" out there, that will give you a "handicap" in each of several short game areas. Used as a guide, you can help prioritize you practice.
For example, if you had a full handicap of 6, but your short game handicaps were around 2, you WOULD want to make your priority your full swing. This kind of player may not be hte majority, but they are out there.