Dear Miss Snark,
I was wondering if you could address the subject of non-fiction books and whether it works the same way or differently to the fiction business. For example, do you need to complete the book first or can you sell on the basis of a proposal?
I have no previous books published but I am a journalist with work published in magazines and national newspapers in both Australia and the UK. I am a general reporter so I don't have any more than a passing expertise in the topic I want to write about however my research and writing skills are solid. Would this be enough of a history to query on the basis of a proposal?
I also aspire to writing fiction and I can see the value of completing a novel before seeking representation and sales. I am not sure whether non-fiction is the same since with my journalism I am used to working to commission.
Most non fiction is sold from a proposal not a finished manuscript. The question you're going to run into though is not how well do you write, but what's your platform..ie what do you bring to the table in terms of access to the media, or outreach to book buyers. Having a platform means you have an established speaking career, a blog/website that reaches hundreds of thousands of people (Miss Snark reaches less than 1/20 of that number daily to give you an idea of what you've got to be able to do), or an established media presence.
Serious academic non fiction may be the exception to this but you better have a job at a university if you want to be taken seriously there.
When you look at folks like Sebastian Junger, his "platform" is that he writes regularly for Vanity Fair, so journalism can work for you but it's got to be the very very top magazines.