Twilight Sparkle begins school in Ponyville. After things don't go as well as expected, she decides there is only one thing to do: get her cutie mark. Maybe she can get some other ponies to help her. After all, some things are more fun with friends, right?
Part of the Shiny-verse (and an attempt to create the Cutie Mark Crusaders).
Also while not a direct sequel, it does reference Boasts and Brag