gas shutoff
I was taught to shut off the oxygen first, although
see:
Cutting Torch FAQ - Baker's Gas & Welding Supplies
says they don't care. If the tip was adjusted correctly in the first place you wont see the little carbon feathers all over the shop in the first place. Besides that there is to much noise around us anyway. After suffering with tinnitus for 30 years, I wish that I had done EVERYTHING that I could have to reduce ambient noise.
I had also been taught to unwind the screws in the regulators after I finish using them... but in any two stage regulator there is no way to unload the high pressure knock down section of the regulator. If this causes any wear... I have not noticed it.
I started using Airco 2 stage regulators 40 years ago. I have rebuilt them a few times over the years. I also will buy any one of them that I find at a flea market or automotive tailgate sale, typically buying them for 10 to 20 bucks and add about 25 bucks worth of parts to make them good as new.
The slamming of the seat... as I stated before the first stage is spring loaded all the time by design, you can't unload it and the proper procedure for re pressurizing the regulator is to stand to the side of the possible projectile path of the internal parts and SLOWLY open the high pressure valves on the tanks. This applies to flight path of the gauges also... that being said, I have never seen a regulator come apart. 42 years of construction sites represents a tremendous exposure to abuse of tools by the uncaring soles that work around you every day.
I turn off my tank valves, and leave everything else alone. If the hose and torch de-pressurize in less than a day I start looking for leaks because what's leaking while I'm away is still leaking while I'm using it. You can test your torch valves by simply submerging the tip in water after turning it off (please let it cool off) to verify that the torch valves are holding.
Paul