Choose a topic for your book. Let your imagination run wild. Write down all of your thoughts and ideas. Tara Lazar suggests participating in PiBoIdMo, short for Picture Book Idea Month at http://taralazar.com/piboidmo/. Each day, write down one idea for your book. At the end of the month, pick your best idea. You should have an underlying theme: love, friendship, fitting in. Avoid overdone topics like a new pet, a new baby or a new home.
Consider the length of your manuscript. Picture books are usually 32 pages in length. When you account for the end page, the title page, the copyright page, etc. you are left with 24 pages for text and illustrations. Therefore, plan for about 12 double page spreads. Emma Blackburn, picture book editor at Bloomsbury Publishing (www.writersandartists.co.uk/writers/advice/327/dedicated-genre-advice/writing-for-children/) suggests a mixture of double page spreads, single page images and vignettes.
Rhyme only if you can do it well. Tara Lazar says that many rhymes are either forced or exhibit inconsistent metre. Don't let rhyme dictate your story. However, if you are an expert at rhyming, go for it. Follow the masters: Jane Yolen, Jack Prelutsky, Karma Wilson, and of course, Dr. Seuss.
How Do Dinosaurs Say Merry Christmas? by Jane Yolen courtesy http://www.scholastic.ca/titles/howdodinosaurs/images/How_do_dinosaurs_say_merry_xmas_spread.jpg.
Keep your manuscript under 1000 words. In fact, the ideal length for a picture book these days is 500 words. Books that are 800 to 1000 words tend to be harder to sell. Tara Lazar reminds you not to be overly descriptive; let your illustrations do the talking.
Maurice Sendak's Where The Wild Things Are courtesy http://media.creativebloq.futurecdn.net/sites/creativebloq.com/files/images/2012/11/wildthings.jpg.
Don't preach. Share your underlying theme, but don't beat it over the reader's head. Begin your story with a unique hook, to catch the reader's interest.
Read as many picture books as you can get your hands on for inspiration. Ms. Lazar recommends reading 500 picture books before you even start your manuscript. Examine the cadence and rhythm of the stories. Look not only at what is said, but what is left unsaid. Look at how tight the writing is. The tighter you write, the lower your word count.
Choose a strong, appealing protagonist. Is he or she loud or shy, funny or scary, friendly or cold? Make sure you develop your main character enough to keep your reader hooked. Give him or her a name that reflects his or her personality or gives a hint about the story. If possible, think about a string of adventures for your protagonist for a possible series. For example, A Pocket for Corduroy features Corduroy Bear, a bear who wears corduroy overalls.
Devise a plot that leaves the reader wanting more, that makes the reader want to turn the page. Keep pacing in mind as you write. While your beginning should catch the reader's interest, your ending should leave the reader satisfied. Include an unexpected twist as Rosie Reeve did in her story When Tom Met Tallulah (http://www.amazon.ca/When-Tom-Tallulah-Rosie-Reeve/dp/1408836998).
Design a striking cover. Emma Blackburn prefers single images to scenes. Make your title snappy and reflective of the story ex. SH! Don't Wake the Royal Baby (http://www.amazon.ca/Shhh-Dont-Wake-Royal-Baby/dp/140884463X) by Martha Mumford, is about a royal baby's life in the palace.
Design illustrations that are reflective of the story. Lauren Child, author of Who's Afraid of the Big Bad Book (www.amazon.ca/Whos-Afraid-Big-Bad-Book/dp/0786809264), provides a combination of creative design and strong text in her picture books.
Know your audience. Prepare a dummy book and test it out on children. Ask for feedback about the title, characters, plot, etc.