By moving slowly, you prevent yourself from reacting impulsively or being overcome with emotion. You allow yourself time to think about the next words you plan on saying or the next action you plan on taking. Though quick speech can give the appearance of confidence and assuredness, you should use it sparingly—it can just as easily humiliate you because you decided, impulsively, to say something unreasonable.
Reinforce this with your physical activity. Move slowly. Perhaps slow isn’t the right word, but cautious. Pick up your belongings with careful attention and put them down the same way. Move about a room with precise intentions. Allow your eyes to be under control, and carefully scan the room rather than dart back and forth to whatever draws your attention at the moment. All of this is to help you act with intention.