Many writers develop rules to help them write.  Sometimes such rules embody almost inhuman abilities in areas such as discipline.  Anthony Trollope would write several hours every morning, no matter what.  Once he finished a novel while he still had time allotted to write.  So without waste, he started on a new novel.
Two years ago, the British newspaper “The Guardian” asked several prominent writers what rules proved useful for them.  Some of them offered great advice.  Zadie Smith has a rule about writing on a computer that disconnected to the Internet.  Elmore Leonard crosses out anything that a reader might skip. Margaret Atwood’s advice is to bring pencils to write on flights, as pens tend to leak.  Roddy Doyle has a rule against checking on for books you haven’t written yet.
Some writers have rules for what they will write about.  Francis Spufford wrote about himself:
I’m a writer of non-fiction who is creeping up gradually on writing novels. I write slowly and I always move to new subject-matter with each book, because I want to be learning something fresh every time, both in terms of encountering history and people and thinking which are new to me, and also in the sense of trying out a new way of writing. My idea of a good project is one that I can only just manage. I’ve written a memoir of my childhood as a compulsive reader, an analysis of the British obsession with polar exploration, a book about engineers which is also a stealth history of Britain since 1945, and […] “Red Plenty“, about the moment in the early 1960s when it looked as if Soviet communism really might be beating the capitalist west in the race to abundance.”
“Red Plenty” is a great book and will have blog posts of its own.  By the way, Francis Spufford has just published another book “Unapologetic”, which is about his being a practicing Christian.