There is only one bit of advice you need when you own your own tanks: bring them to a professional for filling and regular inspection.
Tanks are required to be visually inspected once a year, which involves removing the valve and looking inside for signs of corrosion or damage. If the tank is deemed safe, an Evidence of Inspection (EOI) sticker is applied to the tank showing the date of inspection.
A hydrostatic test is required every 5 years, which determines the tank’s ability to contain pressurized gas. A certified hydro test facility will stamp the shoulder of the tank below the valve with the date of pass.
This inspection makes it easy for you to know if your rented tank has been properly maintained and inspected. If the hydro test stamp is more than 5 years old or the EOI sticker is more than a year old, don’t accept the tank.
Corrosion is the major culprit in tank degradation. Scuba tanks are filled with very dry air, to prevent moisture from rusting the interior of the tank. That is why certified divers learn never to leave a tank empty. Always leave at least 100psi of pressure in the tank at the end of your dive, so no moisture can get in when valves are opened.