To be frank, I have never had any professional training in photography. But you do need to assist a photographer to learn the tricks of the trade. That is very important.
A course can only give you technical knowledge - the theory part of it. Finally, it all boils down to your eye - how you look at things, your approach. The course cannot teach you how to visualise. That is your input as a photographer.
What differentiates the work of one photographer from the other is basically his eye. His way of looking at things. Technically everybody learns. Finally, it is your style, approach or composition that will set you apart from the rest.
I believe to be a commercial photographer you don't need to know how your roll is processed or even the history of photography. You should know what you want as the end result and you should be able to explain that to your printer. I didn't need to know when the first camera was invented. Although I did want to do a course in photography from Santa Barbara, it was too expensive for me at that time.
A photographer tells a model what to wear, how to do the hair and the makeup. For that I attend fashion shows to see what clothes are in. I also surf the net a lot. You have to keep up with the latest both in terms of technique and the gadgets. I also watch a lot of foreign film to see camera angles and techniques.
Stars were used to studio shots where they were made to look overly glamourous and very staged. I introduced the outdoor pictures. I shot the stars on road dividers and bars.
Of course, I took a lot of flak for it. Film magazines said it's a phase. "The stars will cooperate with you for 2-3-6 months. What will you do after that? This outdoor thing is not going to work." But on the contrary, there has been no problems so far. I also did a lot of black and white pictures."
You need inspiration to drive you. The day you feel you are stagnating, you might as well give it up. When I am bored, I go and buy myself a new camera or lens. So that there is some excitement in my life. Then I am all charged to use my new gadget and see the results.