If you want training, go to a real shooting class taught by a reputable instructor and practice what they tell you.
This is true, but it has its own limits.
Not everybody can afford regular refresher courses.
And without them, your practice and application of their tactics and techniques can drift away from what was meant.
Also, it can be hard to muster up the enthusiasm for solo practice, especially to practice the stuff you do worse at instead of the stuff you do well.
There is no one perfect answer unless you are a highly trained, frequently retrained professional, or are in such a hazardous environment that you have a lot of incentive to get and stay good.