Be prepared for A LOT of girls. They are expecting something around 800 girls AT LEAST to be attending. Also be prepared to dance your butt off. New people in charge of the parade and they won't everyone to be able to move.
Yes, smile A LOT, have a pleasant attitude, and be polite and outgoing. The competition for these roles is fierce, so don't be upset if you don't make it. If you don't, just plan on the next audition. Or, don't be afraid to audition for a parade tech role. There are several parade performers who started in parade support, and eventually became a parade head or face character.