To teach a challenging yoga pose think about comforting students, and then sparking curiosity.
Ask students to begin in a position that is relaxing, like an easy seat. This is a chance to explain what will happen before demoing. Giving students an opportunity to relax their bodies before starting sets a chill tone for class and therefore make them feel less in the spotlight for what they are about to try. Your tone of the instructions, both spoken word and sound of voice, should be equally encouraging as well as casual.
The instructor then demos posture cues in clear view. Move to where students have the best angle to see you in the room. Remember to do the pose on the opposite side as the class if you are mirroring the students by facing them. You may not necessarily pause class to have a session on the pose however it would benefit the students if you mirror them and join them in the same effort. General cues will help students get into it; say these while demoing and then again when cuing students into the posture.
Teach to the mid-line. Once in the posture give options to deepen or modify. Be sure to take a variation or offer blocks so most students are able to achieve some variation of the pose in class. Two examples are to have your foot by your ankle in Tree or to keep your toes on the ground in Crow. Seeing the instructor take these modifications can also be encouraging for students who need these adjustments.
In summary, there are 4 main things to remember. Setting a positive tone before starting, talking through the pose, showing the students the pose, and offering modifications can help students cross the mental threshold of a challenging yoga pose.