DO NOT USE SOAP! You'll have a hard time getting it totally rinsed, which in turn will kill your head retention. Just last week I completely disassembled my kegerator set up for a thorough cleaning. Fill a keg with warm beer line cleaner (BLC) and run it through all your lines (you may even consider replacing the lines) and through the tap faucets. I also took all my faucets off, took them apart (they break down to 3 or 4 pieces) and soaked them in the BLC too (you can use PBW or OxyClean if you need to clean them first). Scrub all the parts with a small brush. Then put it all together and run water through your system for 1 minute to flush the BLC. It can be a decent amount of work, but I really only do this once a year and it will improve the quality of your draft beer.
Good luck, and let us know if you have any other questions.