Prepare the church for mass:
Open the building an hour before mass
turn on lights
lay out appropriate altar linens
check Holy Water vessels - fill if needed
Prepare the bread and wine
Turn on microphone system
make sure books are where they need to be
light candles
The Pastor or Liturgist will provide overall supervision and support, there is generally a head sacristan who helps with scheduling and communication but those scheduled can trade among themselves if they have a conflict with their assigned day.