I think in principle the "decide where you want to go with the image" advice is sound.
But that is not how I learned to work in a darkroom and that is not how I learned to use Photoshop. I learned the various processes which would be useful. This is how you develop film. This is how you load it in the enlarger. This is how you decide what crop you want. This is how you make sure it is sharp. This is how you make sure to find the right Exposure. This is how you can adjust the contrast. This is how you dodge and burn. Etc.
Once I had the basic tools, I would look at my images and make decisions about what would benefit that image.
So I will offer a different perspective and suggest that there are a set of tools and processes within Photoshop which are generally worth knowing if you want to do basic adjustments in Photoshop and there are a larger set of tools which are worthwhile if you want to do sophisticated things in Photoshop. And then there are another set of tools which you might want to know if you want to do artistic things.
As a photographer, there are a limited set of tools and procedures which will be generally useful. As mentioned in a joke above about PS being for designers, I will agree this much: a large portion of the tools and procedures in PS are for graphic artists and designers. But there are still some number (300?) which are useful to the serious photographer-craftsman.
How to learn this set of skills? The best is to take a class from a competent teacher. There are many good videos on YouTube. And many bad ones. Sifting through is the challenge.
The Martin Evening book mentioned above is a good reference. Eismann finally updated PS Restoration and Retouching (with others, who probably did the heavy lifting). The 4th edition just came out on Kindle and will be in print any day now. She also has another book which is old but still useful on compositing.
Julianne Kost works for Adobe and has put out much useful material over the years in video and articles, most of which are free.
Lacking a good teacher, I recommend looking at places you pay for video lessons because the material tends to be much better organized to you can learn skills which build on each other and get some comprehension of a sensible workflow. You will ultimately develop your own workflow. Having someone show you a sensible one will get you started.
Lynda.com was a good starting point for me for a general understanding of the overall tools. You pay monthly and there are several instructors who have overview classes to understand tools relevant to a photographer. This is not a bad place to get a foundation.
There are also some good options on CreativeLive.com. You can see free classes when they are "broadcast" and if you use the app, you can watch any single segment for free once a day. And they have plenty of sales where you can get a good deal. If you PM me, I can send you a code for $15 off a first class (full disclosure: my only relationship is as a customer, but I also get $15 off if you use the coupon).
I have my own preferences for instructors on Lynda and CL. There are some other good sources, but these are the two best aimed at a beginner. There are many good free videos on YouTube for learning specific things, but nothing I have found is both good and systematic for developing skills.
To be clear, I am not disagreeing with the advice above. When you first start with an important image, you don't want to just "fool around in PS" till it looks good. You want to decide what you want to do with the image and then begin.
But...when you are still learning the tools, you DO want to fool around with images, experiment and figure out what is possible. So that, when you are ready to work on a "serious" image, you will have the skills.