I'm new, and I have no idea what I'm doing.
BUT I wanted to create an OC because I can never decide between Rarity and Pinkie Pie as my favorite pony. They're both a lot like me, but in very different ways. So, on a whim, I created Dreampuff. She's a dairy heiress. Her father owns Trotted Cream Farms (or something to that effect -- still working on the name), and her mother was a brilliant actress and painter before her accident several years ago. She has been in a coma since then.
Dreampuff loves shopping, parties, the theatre, art galleries and various activities that remind her of life before her mother's accident. Since her mother loved painting portraits of her when she was a child, Dreampuff has a fondness for modeling. She loves acting as well, but she will often shy away from acting jobs for fear of outshining her mother. She has also recently discovered that she has a knack for interior decorating.
She does have some weaknesses as well. She was raised by a string of nannies and was homeschooled by them, so she never had the typical school experience as a child. As such, she is both confused and slightly frightened by children; she has no idea what to do with them. Her relationship with her father is complicated and a bit strained because he was never around much when she was growing up. After her mother's accident, he just threw himself into his work because he was utterly depressed whenever he was home. It was too quiet, too different, and it just reminded him of his loss. He then tried to maintain his relationship with Dreampuff by essentially buying her love.
Despite being a dairy heiress, she has never spent much time in an actual farm environment, and as such, she is somewhat confused and grossed out by the natural world. I wanted her to be a unicorn rather than an earth pony, but as I have not seen all the episodes (I just watch them as they come out on Netflix), I don't consider myself knowledgeable enough about unicorn magic to have a unicorn OC.