I'm attending a casting hall for a movie - What do casting teams look for? What

Question:

I'm attending a casting hall for a movie - What do casting teams look for? What should i wear?

Its for a sequal to a uk blockbuster.
I am 16 and this is my first casting call/audition. There is no info on appearance (apart from no heels no makeup) and no statement on what to expect! Any hints/tips?
As for clothes: - Should I go basic to draw attention to my skill/face or stand out from the crowd? (There is estimated 1000s to attend)
Its on saturday! - yikes! (Also i have never acted before - any tips?! - i really want this part!)

Additional Details

1 week ago
(they asked for no costumes)

1 week ago
feminine, smartcasual or casual?

1 week ago
...its for harry potter, the part of "lavender brown" ron's love interest, same year as harry and ron

Best Answer - Chosen by Asker: 1 week ago
(they asked for no costumes)