Not much unfortunately. From what I know and learned from research, ballet librettos are a bit different from opera librettos: they are “short written sketches that outline the main components of a narrative like the characters, plot, setting, etc” of a ballet (qtd. from here). The librettist pairs up with the composer or uses an already existing score and creates the story from there. The librettist and choreographer can also be the same person. At other times, the composer already has a story in mind when creating the piece and it’s up to the choreographer/author to develop it in a full ballet. The creative process of a librettist doesn’t seem too different from that of a play-writer actually.
So I think you could begin with the a concept: create a narrative situation, develop a story and its characters, but always keep in mind that you are using a written form to ultimately create a piece for an art form that relies entirely on movement and gestures: the only ‘spoken’ language of ballet is pantomime, after all. Also keep in mind that ballets hardly last more than 3 hours. Then, if you don’t plan to choreograph your story, you can find a choreographer who will work hand in hand with you to bring your libretto to life.
Hope this helps!