Maybe writers who want to self-publish can avoid the mistakes by knowing the problems.
1. Illustrations — The quality of illustrations in self-published books are generally weak and sloppy. They often present visuals that are nothing more that what is in the written word. This "See & Say" approach slows the pacing of the story and bores the reader. It doesn't matter how good your story is if your illustrations are mediocre or worse. They will effectively kill your story. On the other hand, great illustrations will encourage children to keep reading and identify with the characters.
2. Design and Layout — Font selection and art direction make a big difference in how readable a book is. The flow of a story through its pages is important to keep children engaged. Does the layout encourage a natural page turn? Does a reader know where the next line is? Illustrations and type should work together not compete. This causes confusion in the readers head and interrupts the flow of the story. It is kind of like going to a movie and having the person next to you continually asking you questions about the technical aspects of what you see on screen. I see this problem all the time — in all levels of publishing.
3. Overindulgence — We could call this "verbal gluttony" because writers say too much. Since most self-published authors don't have an editor everything ends up on paper. The writer is king in the self-publishing arena and they are often too close to their work to see the flaws. Overindulgence often leads to a "See & Say" book that never involves the reader or asks the reader to think. These books tend to preach their story. The great picture books tend to include the reader almost as if they were having a conversation. The words offer just enough information, the illustrator is allowed to bring new information to the story, and the reader completes the conversation with their own thoughts. Overindulgence just leads to a bloatedand boring story.