@Jb33124
One way to start is to start looking at all the available canon characters, and ask yourself if there is a character whose body shape you really like. Then think about characters from other fandoms that you like - anime characters, fantasy or sci-fi, historical figures. Then think how one of those people would look if they were a pony, and use the body shape of the canon character you like.
Like, Joan of Arc of she were like Big Mac. Or Anne Boleyn if she were like Fancy Pants.
Then find an artist who is doing requests and ask if they can draw that character for you.
Then you’ll be all set for next year if we do this again. Each year there’s dozens of artists who volunteer to create free drawings of people’s OCs for the event, so it’s easy to find someone to draw your OC. And having an idea of what your OC should look like will help you describe your OC to the artist.
That’s just one way. You can also find an online OC generator and just keep hitting refresh until you get something that looks interesting.