Here’s what happens most of the time when I meet new people.
Them: What do you do?
Me: I’m a novelist. I have my own self-publishing company.
Them: Really? I’ve always wanted to write a book.
Me: You should.
That’s right. Write. It’s the first and integral part of the idea or process of writing a book. You have to write. Don’t worry about the proper punctuation, don’t worry about if it’s making sense, just get words to paper. All the other things can get worked out later.
But the sooner you write the words and let the creativity have it’s freedom, then the story will come.
So my first piece of advice for anyone that wants to write a book is the simplest one word answer.