1. Magic is involved. This can be at a high level (Cinderella's transformation - clothes, coach etc) to low level (a little magic is used to help a character succeed at something. This is taken to its logical conclusion in Fantasia though there the character also needed to know how to stop but that's another story!).
2. There has to be a transformation of fortune. Usually from being downtrodden to the happy ever after, but sometimes, such as in The Little Mermaid, the transformation can be seen not to have been what the character really wanted. Or it failed to achieve what it is was meant to achieve. However, the transformation of fortune has still happened.
3. Generally, the good guys either win or fail heroically but leave the banner to someone else. Always true. I would describe a story where the villain won as a a nightmare, rather than a fairytale. Why? Because with the villain winning, you can kiss goodbye to hope. That villain will impose their will on their subjects say with nothing and nobody to stop them. I fail to see the story in that. Re the latter, remember in The Lord of the Rings, there had been a previous attempt to defeat Sauron once and for all. That failed but it paved the way for the story to follow.
4. Inanimate objects should be treated with caution. This can include things like the Portals in the Harry Potter series, any shiny red apple, talking mirrors, and swords/rings etc that seem keen to be reunited with their former owners. These always cause trouble but it is a major element of a fairytale.
5. Expect the unexpected and/or what is unknown in our world to be known here. This is especially true for the existence of magical creatures, universes far far away, and so on.