[header] How to write a fictional story about horses [title] Learn about horses. [step] If someone who knows a lot about horses reads your story, you want them to get the sense that you know what you're talking about. Read up on horses online and at your local library. 
If you can, spend some time observing real horses and interacting with them. If you can't get to a place with live horses, watch videos with horses to get a sense of how they move and behave.