The first part is random memories of growing up in humble beginnings. His childhood was spent with his solo mother and older brother and an innate love of words. He wrote satire about the teachers and sold them to the other children at school. He went on to teach English at high school level for many years. He married a woman who was also a writer and a constant source of support for him.
He advises writers to "read a lot, write a lot". He cites past students who apparently have no time for reading. His advice would be to read everything; that you learn more from bad books than good.
Then he moves on to practical advice on writing and grammar. There is a whole section on grammar with some basics like minimising adverbs and keeping the action moving by using active verbs instead of passive. He advocates leaving some time between writing and editing so you can approach it with fresh eyes. He was told early on to cut the word count back by 10% when editing and still follows that advice. "To write is human, to edit divine". He argues that character-driven books are much more interesting than plot-driven books.
The last part is about his near-death experience in 1999. This section was a real page-turner as he writes with a detached inevitability of what is going to happen. The reader is stuck reading on in horror. I will leave you to find out for yourself what happens.
I realize Stephen King is not everyone's favourite writer. He must be doing something right though, to have sold around 350 million books. I have read quite a few of his books, mostly as a teenager. One of my favourite books ever is "The Long Walk" which is one of the stories he wrote under the pseudonym Richard Bachman. Whether approaching this book as a King fan or an aspiring writer, there are some great points to take away from it. Apart from anything else, On Writing is simply a great read.
"What would be very wrong, I think, is to turn away from what you know and like in favour of things you believe will impress your friends, relatives, and writing-circle colleagues."