If your railing has wooden posts, then you will need to have the posts inspected for maintenance or corrected on an annual basis.
Also check for loose cables and use an allen wrench to retighten any cables that may be stretched.
Cables that have been exposed to the outdoors for a long time may have accumulated a lot of dust, wipe them down.
It is recommended that cables and stainless steel cable railing kits be sprayed annually with a sealant, which adds a layer of protection between the stainless steel and the outside air.
Other than the above there is no other maintenance and you can continue to enjoy your beautiful deck for years to come.