I would probably be mostly creative, but I would have a touch of dreamer, dreaming about all the things I could do with magic, and a bit of prankster, when I test out my magic.
Then, of course, when ever a teacher walks into the room I'd "magically" transform into a teacher's pet. I've never been trouble for teachers (in RL), and I don't want to start now - especially at magic school where all the Masters are highly practiced mages! (Plus, if I'm nice to them, I might get some extra magic stuff - like little tips and maybe some extra lessons. Not boring lessons, but fun magic lessons.)
Basically, I'll be whatever I have to be to get into the Magisterium!