The Lemon Face trick is a technique i use all the time to make the models and people i shoot with more relaxed.
some people can be very stressed or feeling awkward in front of a camera, by using this simple but effective technique you will help them relax and and focus on something else than the camera.
They will have a beautiful face no matter how scared they were, because of muscles memory and tension removal.
Test this with your models and let me know if it works for you.