Sometimes, as a sub, you'll have parents or administrators or even aides or other teachers come into the classroom and observe you. One time I was in a middle school classroom and I had a student who was being disrespectful. I was in the middle of telling the student that if they were not going to be nice, they were not going to be staying in that classroom and that they would be headed to the office, when a woman walked in. I did not stop what I was doing and as the student argued with me, I continued to "lay down the law." The woman gave no visible reaction to what was happening, and continued to stand in the back of the room for a few more minutes. Eventually I got back to teaching and the woman left. I gave it no more thought and went on with my day. 

I knew that the woman worked for the school, but I didn't know who she was or what her role on campus was. 

As I was heading to the office at the end of the day, preparing to leave for the day, I saw the woman again. She walked over to me, introduced herself as the Vice Principal and told me that she liked the way I handled that student and the situation and told me that the school would love to have me come back any time. 

That was the day I learned not to be nervous when people come into my classroom.