As a mom who hires plenty of babysitters, my advice to you would be to smile as much as possible (regardless of what your feelings are) and be willing to help in any way possible and don't be afraid to take control of the situation (gives mother confidence you can manage by yourself). Don't be afraid to ask questions (how they manage problem behaviors/discipline, where the food is, first aid supplies, etc.) and make sure they are on your speed dial.
Good luck!! !