Good question.
The best plan would be to tear down the cylinder until you have the pins, springs, and all the parts spread out in front of you, then to clean them thoroughly in a good degreaser, reassemble, and lubricate with a good silicon/teflon lubricant NOT WD-40, Oil, or Graphite.
That said, if you are not familiar or do not have the tools to do a complete teardown, your next best option is to flush the lock heavily with WD-40, running your key in and out several times, wiping between run-ins. Continue to do this until the key comes out clean. Next, let dry completely, then lubricate thoroughly with a good silicon/teflon, PTFE based spray lube. Run your key or pick in a few times to get the pins working, and you should be set.
