Amy Keating Rogers (Writer of The Last Roundup, Fall Weather Friends, Bridle Gossip, and several others) has answered a whole plethora of questions about the writing aspect of cartoons in general, starting from the school days all the way to our much loved Friendship is Magic! I know there are hundreds of potential authors out there just dying to see what exactly is required for a career like this, so it might be beneficial to give it a look!
Check it out here!