First, just let your mind wander. Jot down any random thoughts or ideas that come to you related to fantasy. Maybe it's a cool magic power, a strange creature, or a mysterious place. Then, try to connect these ideas and see if they can form the basis of a story. You can also talk to other fantasy lovers or join writing groups to share and get feedback.
Start by imagining a unique world. Think about its geography, magic system, and different races or creatures. Then, build characters based on that world. Also, consider what problems or conflicts your characters will face and how they'll overcome them.