In the Runway challenges, your look is put into voting where other players have to decide whether they like your look better, or another look shown to them. With your look, you’re trying to fit the challenge description as much as possible, without considering clothing tags. Your grade is determined by how many players voted for your look.  
 
You can boost your grade by one star by making use of the Unworn bonus – applying to a challenge wearing clothing you haven’t worn in a challenge before will increase your Unworn bonus which adds points to your final score and grade. You also can boost your grade by wearing clothes that have a Trending label on their thumbnail.