Are you an expert at anything? Scuba diver? Snorkler? (Hey, you don’t have to be an expert, but if you’ve done it, you can write about it!) Ghost Buster? (Even if you only see the ghosts and don’t bust them!) Lawyer? Been in the military? Hired a Private Eye?
So this sounds more like writing what you know. But actually, if you can sell an editor or agent on how you know what you’re talking about, that will give you somewhat of a boost in believability, even if you write about the unbelievable!
And that gets into branding—even before you sell. Here we go. I'm at FF&P today, talking about branding.