Great fiction appears effortless to the reader.
The characters and setting are so real, the story so believable, that the reader is completely unaware of the author behind the words. The smoothness of the text belies the hours of hard work and practice that went into its creation. Regardless of the age you're writing for, your first one or two paragraphs set the tone for the entire book. They introduce the main character, point of view, setting, mood, and sometimes the story conflict. Grab your reader instantly rather than boring him or her with unimportant background information.