1. Prepare the topic you want to present in the video lesson well. Concentrate on that.
2. Do not care/bother about the other things troubling you like no physical interaction with students, different age groups and English skill levels.
3. Just be yourself when telling or reading out a story or playing a language-related game.
4. Please be aware about the true function of this video lesson: It is complementary and cannot be real substitute for a lesson with real physical teacher-student interaction. Just be yourself, do not worry. The more authentical you come across, the more this will be appreciated, I am sure.

Good luck!