lemon
juice will clean it quickly, but won't leave the glossy shine that a good polish will do.
What I usually do though, is attach a 510 thread from an old cartomizer (for mods) or a 510 adapter from one of my ohm readers (for attys) into my drill. Then I screw on my device and run the drill while holding some cape cod cloth on it. Then I run the drill with a microfiber cloth to get the polish off. If its an atomizer or drip tip, then I do the last step of rinsing it in the sink, just so I don't get polish in my mouth.
The whole process takes about 5 minutes and leaves my copper in beautiful shining condition. I polish anything that looks dirty and I am not trying to patina at least once a week. Just did my XXIX, FUhattan, Paragon, and Vapetasia drip tip yesterday. They are so shiny!