DHS recommends that you precut plastic sheeting for any windows, doors, vents or openings and label them appropriately. The plastic should then be stored with duct tape and scissors in the designated shelter-in-place room so that it can be quickly accessed and installed.
DHS does not recommend that you install the plastic sheeting in advance. You can, however, make sure that any areas that can be permanently sealed such as where pipes come out of the wall or where trim meets the floor and walls, are properly caulked. This will also help reduce heating and cooling costs so is a good idea overall.