If the business is charging money to detail customer vehicles, nothing teaches you more than actually doing it i.e. practicing the techniques gleaned from researching or gaining the "training" of proper methods. What you have described is somewhat what i have done and still do. The key is being a good student. Carefully and intensely studying what you are doing yourself with the information you've read, listened to and watched on videos. Understanding the physical principles and learning the science and mechanics of the actions is, to me, what is most important. Read, listen to and watch those concepts and techniques and then put the tools in your own hands and practice, practice, practice! then carefully studying and scrutinizing what you just did. Either you did it right or wrong. If the latter, figure out why.
I supect a lot, if not most, of us here learned the same way you are. I am sure the best...and I mean the BEST...method of training is Mike's CR Course but i can't really swing that cost myself. The only other way is to teach myself and I will humbly say, without any implied conceit, I have developped the skill to give my customers incredible value through my services.
Another valuable aspect is to get involved. Immerse yourself in this business with personal contact with others that do it. I have met with others both in my area and outside and discuss, do, see etc. There are other successful perspectives from others that can enhance your mind and widen your knowledge base. Personnally interacting is different than reading something or viewing something online.
Then KEEP LEARNING! This remains a very progressive pursuit of knowledge. There are always new things to learn but for the time being you can make money doing it with self training and proving to both yourself and your customers you know enough about it to make some money.
I did.
