I wind up turning everything off, including the cylinders, then disconnecting the lines from the cylinders. Now reconnect the lines and SLOWLY turn on one (or both) of the cylinders.
At this point, the propane in the lines may have been evacuated, pressure reduced, or air/propane mixture disturbed, so auto-striking appliances like fridge and water heater may give you some trouble initially. Help this out by turning on the stove top and use a match to get the flames started. Once they're burning nice and blue, you should have fewer problems with the auto-strike on fridge and water heater.