In addition to all the advice you received here, I will add the following. I have attended Canadian Championships and found this to be useful. Please be kind to the security staff at the doors. I go to all practices (even early morning ones) and after the first day, the security staff will start to recognize you and will let you in the building so you won't freeze outside waiting for the doors to be unlocked. They can also be helpful if you need a taxi (they could often recommend a good company as well as offer great places to eat!
Have fun! Be respectful to skaters, coaches (don't interrupt them when they are with their coaches, and don't be afraid to say hi if you see them warming up in the arena.