Which fairytales are you drawn to the most and why? Can you visualize one of your characters as if they were a fairy tale character?
Your entire story or novel does not need to be similar to the fairy tale. However one character can have striking resemblance in their personality or their situation to the fairy tale.
Think about how this impacts character dynamics and how you can utilize the underlying themes of the fairytale to your advantage.
Fairy tale themes have stood the test of time and hence if the throughline of your story runs parallel to one, then perhaps you’ve a good story!
For example, is X in your book just like Cinderella or Red or like the emperor with new clothes?
Can you write a scene where you demonstrate the above?