A fairy tale always contains a mythological or magical element. This might be the characters, settings or events. For example, "Cinderella," a popular fairy tale, features a magical fairy godmother who grants Cinderella's wish to attend the royal ball. This includes a spell, which provides a magical carriage, that expires at midnight. Fairy tales can take place in fictional realms without regard to traditional chronology. They also can include such magical elements as fairies, goblins, witches, magicians, magic spells, superhuman abilities, castles, and mythical creatures and places. Create detailed magical and mythological elements to incorporate into your fairy tale.
A fairy tale includes universal themes, such as love, overcoming adversity, justice or coming of age. Universal themes are concepts everyone is familiar with, no matter what their background. A quest theme, or a series of events a main character(s) goes through in order to grow up or gain wisdom, is most common. While you're writing about magical characters in magical realms, include the realism of life experience, which transcends reality and fantasy. This might be written as a character overcoming fear, conquering evil or injustice, or finding love. Whatever your chosen themes are, use the events of the story and the actions of characters to convey those themes.
Have a clear beginning, middle and end to the story. Although any story can be a snippet or a glimpse of a larger story, a fairy tale should have a clear beginning and end. The midpoint is usually a turning point in the story, when something happens to motivate a character to take action. A good ending includes a resolution to any problems and emotional closure for readers. It does not have to be the traditional (and now cliche) "and they lived happily ever after," but it should give readers a sense of conclusion.
The technical composition of your fairy tale should be top quality. So, as with any writing, be sure to proofread your work. Make sure the grammar and spelling are correct, and ask peers to read or edit it. A second pair of eyes will almost always help improve your writing. The final copy of your fairy tale should be free of typos and errors, especially if you want to publish it.