Once you've plotted out your book, developed the characters and written the last word of text, the real work begins. As busy editors are bombarded with hundreds or even thousands of submissions a year, it's more important than ever that authors apply their own editing skills to their manuscripts before putting them in the mail. Checking your basic grammar and spelling are of course important, but authors need to go beyond surface editing if their work has a chance of catching an editor's eye.
* Trim, tighten, hack away. First, second and even third drafts of manuscripts are almost always laden with extra words and scenes. Take a break from your book and then read it through with a fresh eye. Write down your theme in one sentence (what the book is about, such as working through shyness on the first day of school or showing how Thomas Edison's childhood experiences influenced his adult life).
The plot (or progression of facts and events in nonfiction) is your vehicle for conveying the theme to the reader. Ask yourself if each character and scene advance the plot toward communicating this theme. And decide at the beginning that you will give up your precious words and finely-crafted scenes for the betterment of the book.
Pithy dialogue may be fun to read, but if it pushes your story off track, it's just a literary dead end. Take the publishers' suggested word limits seriously: no, you don't really need 3000 words to tell your picture book story about Freddy the Frog's adventures in the Big Pond.