The possibilities are endless!!! Think about your dreams for what you want to happen with your future in horses and write about that! Or write about some things that have happened to you but in a more interesting kind of way - maybe even exagerate a little. I love writing and I have written lots of horse stories. Perhaps the best one was of a misunderstood horse called Tranquility (Quill), no one could get anything sensible out of Quill until this girl came along and figured out why Quill wouldn't cooperate... kinda long story so I wont tell it here! But write about something you love - that's always the best way.
A Girl is really lonely and on the way home from school one day she can hear a horse neighing and so she finds this horse, she begs her mum to keep it and her mum says yes, someone (dont know who yet) goes missing and the girl and the horse work together to find the girl, who has been bitten by a snake somewhere.
Because I want the girl to be part of a riding club the girl finds the club as she hears horses on the way home from her new school, when she gets home she gets changed and tells her mum she's going out with a new friend she's made (as a lie) and she goes and has a look at this Riding Club. When she gets home she tells her mum and because her mum wants her daughter to have a good time and make brand new friends her mum lets her join, when she's at the school a horse and a girl go missing and the new girl and her 2 new friends go to find the girl and the missing horse.