One way is to observe the world around you. People's behavior, conversations, and the environment can all spark ideas. Another is to read a lot. Different books can inspire you with their concepts, characters, or writing styles. You can also draw from your own memories, both good and bad.
You might consider a story centered around a mystery. Maybe a disappearance or a crime that needs to be solved. This can keep readers on the edge of their seats as they follow along with the investigation.
One idea could be a haunted house where every night at midnight, the walls start to ooze a strange black liquid that whispers the names of the previous owners who died mysteriously in the house. The protagonist could be a young journalist looking for a big story and decides to stay in the house for a night to investigate.
One idea could be a story about a young orphan who discovers they have magical powers. They then embark on a journey to find out their true origin and along the way, they make friends who are also outcasts. Together, they face challenges from those who want to use their powers for evil.
One way to write a fantasy fiction story is to start with a prophecy. For example, there's a prophecy that a chosen one will be born with a special mark and will defeat an ancient evil. The story could follow the journey of this chosen one as they grow up and discover their powers. Or, you could create a world where dreams are real and people can enter other people's dreams. A thief could use this ability to steal secrets from the rich and powerful. Additionally, you could write about a group of adventurers on a quest for a lost city full of treasures and magic.
Set it in a different time period like the 1920s. Cinderella could be a flapper girl who dreams of going to the big jazz parties but is held back by her step - family. The 'prince' could be a rich jazz musician. Instead of a glass slipper, she might leave behind a beaded headband. And the fairy godmother could be an older, wise jazz singer who gives her the confidence and the right look to attend the party.
You can get story ideas by observing your daily life. Simple things like a conversation you overheard or a strange event you witnessed could inspire a story.
Imagine a world where people can exchange their dreams. A person who is always dissatisfied with their own dreams decides to trade with others. But they soon realize that each dream has its own problems and that the grass isn't always greener on the other side. Through this experience, they learn to appreciate their own dreams and the unique experiences they bring.