Most fashion designers typically require their models to not smile when walking the runway. The idea is that the audience should look solely at the fashions and not concentrate on the model’s face or personality. Models become walking mannequins; period! The exception would be a designer like Betsy Johnson whose fashions are all about having fun with lots of craziness on the runway.
Commercial print modeling is all about selling a product and most models are required to smile and look friendly. Local department fashion shows are more relaxed and you will see lots of smiling models walking the runway. The same applies to promotional models where it’s all about personality before looks (THINK QVC).
If you are booked for a runway show, the designer and/or choreographer will tell you precisely what type of facial expressions they want you to project on the runway. Of course, you can also consult with your agent for their advice too!
And lastly, when presenting yourself for any type of audition, be sure to smile and show your personality!