This really is an important issue. Way too many teaching pros and amateur range gurus will tell you everything that is wrong with your swing. I include self diagnosis in this.
In a word: HORRIBLE!!!!!
Not only is it bad because you can’t think of so many things and implement them in the approximately one second a golf swing takes place…there is a bigger issue.
When you fix the first problem in your swing, it affects how the rest of the swing works and you may eliminate any or all of the problems that occur after that. So working on more than one problem at a time is not only way too demanding mentally, it is ineffective.
Even worse, you may make some of the problems double in the negative column by working on more than one at a time.
Here is a video that some of you may not have seen, but it gives a very elementary demonstration of why you should only work on one thing at a time. Sometimes just a setup change will be enough to start with…showing that you should attack the problems one at a time in the order they occur and hopefully eliminate some of the subsequent ones automatically.