There are hundreds of books and thousands of books and millions of opinions about what is important in the teaching of writing.
After 30+ years as a high school English teacher, with a few doubling also as a college instructor, these are the things that I have settled on as essentials, for me.
In addition to these 5, there is always the understanding that reading, writing, and thinking are inextricably and recursively interwoven. Writing is the commemoration of thought on paper (or whatever medium you choose). Readers write better, writers read better, readers and writers are better thinkers.
PS – This list, by Charles Whitaker, is a good list of best practices.