Good cloud fanfiction starts with a clear idea of what the cloud represents in your story. Is it a symbol of mystery, or a source of power? Develop a strong plot that involves the cloud in an essential way. Also, pay attention to the setting. If it's a cloud - based world, describe how things work there. And don't forget to give your characters distinct personalities that are affected by the cloud elements in the story.
When writing cloud fanfiction, it's important to do your research if you're basing it on real - world cloud concepts like cloud computing. But if it's more of a fantastical cloud, let your imagination go wild. Build tension and conflict around the cloud. Maybe there's a villain who wants to control the cloud for evil purposes. And use dialogue to show how the characters feel about the cloud and each other in relation to it. Make the reader care about the cloud and what happens to it in the story.