Inspect the tank, regulator, and O ring or washer for any visible damage.
Using an oxygen wrench or valve stem on the top of the cylinder, turn the valve counterclockwise to slowly "crack" the cylinder for 1 second.
Attach the regulator/flow meter to the valve stem using the two pin-indexing holes and make sure that the washer is in place over the larger hole, do not overtighten.
Attach the oxygen connective tubing to the flow meter.
Check for/correct any leaks. Check for adequate pressure in tank.
Open the O2 system by turning the valve stem on top of the cylinder or using the wrench, counterclockwise
Set the regulator to the proper flow based on the delivery device.