Roll the dice get inspired with broad strokes for a backstory that you can fill in the fine details on.
For example you have your characters in your story, but need a way to introduce them and show how they interact with each-other in adversity.
You roll an apple with a worm, a moon, and a candle.
Put your characters into this situation where they are hungry, its night, and all they have to eat is a rotten food, what would they do? How did the food get rotten? What happens when the candle runs out? These are all good prompts, and the actions you give your characters may surprise you, and help you make their motives more clear.
Even if the scene you describe does not make it into your final story, it will help you work through writers block, and define your characters.