The blog The Rejecter has some good advice for you one what not to do when crafting your book's query letter. Namely, don't discuss your potential audience (3. "My detective protagonist lives in an RV home. 4.2 Americans own RVs, and I think this book will appeal to them." [Yeah, I'm more likely to buy a novel that has a main character living in the same type of home as me. That's a definite sell right there.]) and don't compare yourself to other authors who are just like you except that they are published and rich.