Here are some options to set up your Green Screen.
Lighting: even lighting is the key. Try not to have one side or edge brighter than the other.
Placement of people in front of the screen – try not to have students stand against the screen. This will create a shadow on the screen that is difficult to remove. A usual rule might be to have them extend their arm as the distance marker from the screen.
(Note: Log into your O365 account to view the videos.)