Decide what lesson your fairy tale is going to teach before you write it. At their core, fairy tales are morality tales from the horror of stepmothers to not talking to strangers. They are generally teaching something and yours should do the same.
Create a good character. A fairy tale needs someone to root for. They don’t have to be perfect. Just think Jack in “Jack and the Beanstalk” or Red in “Little Red Riding Hood” but your readers should like them and want them to succeed.
Devise an evil character. A fairy tale must have an evil character that works as an antagonist to the good character. The evil character usually has special powers of some sort and they must use those powers in a way to cause the good character pain.
Design a magical character or object to write into the fairy tale. The magical character can be the evil character but many fairy tales have both good and evil magical characters that work to off-set the other’s influence.
Step 5 Identify what obstacles your good character is going to have to face. Whatever the obstacle, it should seem insurmountable and genuinely require a bit of creativity by your good character and a little magical assistance.
Write a happy ending. A fairytale isn’t a fairytale unless it has a happy ending. Your good character must succeed and your evil character must lose and lose in a big way so you can write your “happily ever after.”