How do you write non-fiction?

I’m researching and writing a non-fiction book, about preparing yourself to survive climate change. I started writing it because I thought it was an interesting topic, one that hadn’t been covered elsewhere in any depth, and one where I have a bit of expertise (thanks to three years as environment editor at The Conversation). A publisher thought it sounded OK too, and gave me a contract, a small advance and a deadline.

I’m pretty sure this is how you write anything, right?

Several months in, it’s dawning on me that I have no idea how to write a non-fiction book. I can write a short essay (if writing about reading on the toilet counts). I can write, kind of, a fiction book (you just make it up, right?). And I figured the skills I’d picked up doing both of those would see me through writing 80,000 words of factpinion. But I’m not sure anymore that’s true. I mean, I don’t even really know how much fact should be in this book, and how much opinion. And I don’t know how rigorous the facts should be. Are there rules?

Over the years I’ve read no end of advice on how to write, but it’s always been directed at fiction writing. And some of those things do still apply for non-fiction: sit down regularly at your writing instrument and put words on it, whether you feel like it or not. Don’t be boring. Cut stuff that doesn’t advance the narrative. But that’s about it…

So does anyone have any tips? Y’know, pithy aphorisms that I can stick above my desk to keep me on the straight and narrow? Help!