When I did my first demo lesson in a fifth grade classroom during grad school I was a nervous wreck. Being up in front of the classroom for the first time can be so terrifying, but I learned so much and there was one tip in particular that I will never forget, especially because it seems like such a small thing.
Never turn your back on the class when you are talking to other students.
I had been checking in with a small group as they we were working, and had leaned over to get down to their level to chat. However, in doing that I had my back completely turned to the rest of the classroom, which is obviously a recipe for disaster.
When you check in with your kids make sure you always have a full view of the entire classroom. Choose your angles carefully!