The vital step when teaching someone to write is to convince them that it's not chaos: planning, working through ideas, outlining, drafting, and editing really can lead to a superior product, so long as you are willing to put in the time and the effort.
The vital step in writing professionally is to recognize that chaos defeats the method every time: meticulous planning, careful drafting and revision, and whether you say what you intend (or do better!) depends on moments of inspiration that resist that plan. And whatever you write, you will find ways to say it better, later. No writing is ever done, just finished, and the willingness to let it go is most important.