Usually, you would start by making sure the room is ready (temperature, music, props, and materials). This is also a good time to get to know any students that arrive early as well assess the mood/energy level of the class. It is important to be aware of injuries, and conditions such as pregnancies, therefore modifying your plan accordingly. If the students are new to yoga, you maybe demoing up to 50 to 75% of the class. If they are more experienced, you are welcome to walk around and give more nuanced instructions.