I think you should look like an ad for a hair product, those girls always look fresh.... start looking in mags for makeup ideas. You can wear makeup, just pretty, think not glam just pretty. Think SI Swimsuit issue makeup- thats beautiful,naturla, sunkissed, and bright eyed!
I would go as you naturally are, on any old day, unless the casting says, Curly hair model, or straight hair model, or casual, or sexy...then you would know how to change yourself and look.
I think it is a simple thing, nothing to be dwelled upon, don't need to spend hours changing your clothing a million times or fussin with the hair... I usually get my face done on the train.. haha. when I go to a casting I just go wearing something I love...even if I just wore it yesterday.. I like being comfortable and myself, even if it means I am in heels or a dress.. I try to look like the ad and model they are looking for...but your compcard should show your diversity. YOUR PHOTOS, your compcard should show your LOOKS if you have many.- for example if you hair can be both straight and curly then.....you should show your hair straight and also curly on your compcard, and your different looks,- from wearing a dress, to wearing jeans... doesn't have to be MAJOR extreme.
You will notice that ALL types come out to auditions and castings, sometimes the totally different looking than you. And sometimes you book a job or don't book a job because you just weren't what they were looking for, or you were. Even a hand modeling casting is competitive, any type of modeling is! So it is best to focus on your compcard, because what you wear to the casting is small compared to what you will leave when you are gone and out of the casting directors face....will they remember you?