One of the best ways to maintain your cables is to properly lube it. There are many ways to do this and the one that I am most familiar with is to dismount the cable/housing from the braze ons and slide the housing up or down, then apply lube on the cable. But if you want to speed up this process, you can use one of these thingies, its called a Cable Luber.
With this tool, you can place it right how the picture shows, take your favorite spray lube with one of those red spray nozzles and insert it to the red straw, spray! There’s nothing really to it. These luber tools can cost as little as $10, and can be found all over the Internet, especially Ebay. You could also find these things at a motorcycle parts shop or dealer.