Recently there was an interesting, if depressing, article in the Guardian, about the "slush pile," the unsolicited manuscripts that are submitted to publishers. The writer, Jean Hannah Edelstein, took a job sorting through one such pile and started with the hope that she would discover some unknown work of genius. The truth she says, was very different.
She cites a few examples of submissions, including ""We are a normal Leicestershire couple, until the lights go down. This is the true story of our erotic journey, illustrated with woodcuts." "I am a 35-five-year-old mother of four children and two dogs and I have an unfortunate foot rash. I have written a novel about a 35-five-year-old mother of four children and two dogs who has an unfortunate foot rash."
She has a special warning for writers who aspire to pen children's books: "Often, the most awful stuff was written by aspiring children's authors. It appears to be a widely-held notion that anthropomorphising pavements, natural disasters or household appliances is the way to secure a place in the children's canon. But while your grandchildren may appear to really enjoy Tommy the Tenacious Toaster, the chances of it charming anyone else are slim."
A few other points she made, which I will summarize: Most bad manuscripts are already bad in the first five pages (and the cover letter); if the book is bad, sending photos of yourself, letters from your mother atttesting to your genius, etc. will not help; neither will phoning up the person who rejected your work, in order to argue with them; and if you suspect that the reader didn't get to the end of your (bad) manuscript, you're probably right.
In the midst of all this gloom, however, she also admits that she can be wrong. A book she rejected twice later was published by another company.