An increasing number of query letters fail to say what the book is about in any meaningful or compelling way. There's a cursory set up paragraph "hot shot detective must solve crime or face social isolation!" What those letters cover instead are the marketing possibilities for the book.
Let me be clear: marketing is important, but it's not what I want to know about first, or even most.
You MUST tell me what the book is about, and tell me about it in a way that is compelling.
I don't want to see "film" "best seller" or "niche market" or "studies have shown" anywhere in your query letter for a novel.
If you don't tell me what the novel is about, I will send you a form rejection. I won't waste a moment of regret on it either because I want to work with writers who are prepared, and careful, and meticulous
Of course, the people who are doing this have never read this, or any other blog. They've certainly never availed themselves of the hundred or so examples at QueryShark.
For those of you who are now panicking that you've tried to write a good query, and are afraid it won't show: stop worrying. You'll do just fine. You'll do just fine because these mistakes are by people who aren't trying hard to get it right. These mistakes of are from people who are just throwing things at the wall to see what sticks.
If you want to stick to the wall at my office, you'll need an octopus.