It doesn’t matter if you're writing a 70,000-word novel or a 600-word picture book creating an interesting story is simply a task of asking yourself questions. Perhaps the most helpful source for what to ask yourself was penned by Rudyard Kipling (30th December 1865 – 18th January 1936),
“I keep six honest serving-men
(They taught me all I knew);
Their names are What and Why and When
And How and Where and Who.”
The four lines above have helped me on many an occasion. What follows is how I use the above to help me construct a picture book story.
The 'who' is obviously your main character or characters. As a picture book writer this can be animal, human, robot, alien, fairy, wizard, monster, I could go on. Basically almost anything you like. However many an editor will tell you to keep away from talking inanimate objects. Yet Disney still manage to create characters from cars, toys, garden gnomes etc. that children love, so perhaps you can to.
The 'what' can be what happens in your story or it can be what your theme is. For example the theme for my picture book A Book For Bramble is loneliness, missing a friend and how my character Teasel deals with this loneliness. Although it didn't start out as that. It started with me wondering what hedgehogs dream about when they hibernate. But many authors will tell you the first idea they have will evolve and change as they work on the story.
'Why' is linked into the 'what.' So ask yourself what happens and why. For example in my book The Best Jumper the 'what' is Spindle the mouse has a jumper that appears to be shrinking. However the 'why' it is shrinking is because he is growing.
In picture books this is perhaps one of the less important questions. Many of the picture books I've read can be set in any time period. A book about fairies inhabiting a different world could be now or 100 years ago, there is no real relation to ‘our’ time.
Many picture books are set within their own world. For example my book Dog Did It is a mythical world populated by trolls. My book A Book For Bramble could be almost anywhere in the world where a mouse lives in a hole under a hedge. As the author I saw Teasel and his family living in the English countryside. However he would be just at home in any European country or even in some parts of the US.
This is quite a big question. However I normally use it to answer the question of how my character overcomes the problem/issue I've given them. If you're a reader of picture books you'll notice the how to overcome the problem doesn't always work first time. Often the character has to have three attempts to resolve the problem/issue before they succeed.
So what ever you're writing if you're stuck for an idea (plot or character) then why not give the 5 W's and H a go. It works for me, it may work for you.