Edman, I'm not going to say if it is the best way but I used powder graphite on mine when they started sticking. I pulled them out of the handle at the top and worked the graphite down the cables. That was 8 months ago and they are still silky smooth. There may be a better way or a lube that does not attract dirt.
I found the easiest way for me was to unscrew the adjusting ferule and use a spray lube. One of the best lubes I have found for cables is Honda's (sorry) O-ring Chain Lube. It has teflon and molybdenum in it and lasts a very long time.