I did go to artschool and I applied for the filmdepartment. This was in 2001 and artschools tend to look differently at applications than filmschools.
I was expected to bring drawings as well.
So I brought my best work: drawings, a drawn animation, a trailer of a short shot with miniatures and a webcam plus the storyboard I made for it. This way I apparently showed I was creative enough and had some understanding of the medium to start studying there.
Now it's 2016: I don't think I would pass with this, because gear and software are far more accesible than 15 years ago.
Bring your best work.
Bring storyboard you made as well.
If you feel you can do better: create something new.
(Creating something new is always good, btw!)
Make sure you know how much time you've got for your presentation.
And show you've got passion, creativity and energy.
Ask someone who is already studying there about their application.
Good luck!