In all seriousness though...there are special cleaning kits for CDs. You spray something on it and then this kit thing wipes in some kinda special way that doesn't scratch and keeps data from being messed up.
Some stuff is dirty, and some stuff is actually tons of tiny little scratches in the plastic film of the CD.. For just dirt, you should be able to get compressed air, maybe just water and cotton, and do not clean in circled around it, always clean from the middle ring and wipe outwards, then shift the CD and do it again, and so on until you get the whole CD. If it's the scratches, they have some stuff that I know many places sell, including EB games, or Gamestop, I can't remember which.. It's like a white paste and it comes with cloths, and is overpriced there as usual, but it's fixed a scratchy disk for me before.. As long as the scratches are only in the plastic film of course, not the actual metal.. Or not jagged, or weird angled, or other things can be unfixable. Actually, I've had a CD with a huge slit that went all the way through the CD and you could bend it open, but put it back perfectly and it still worked.. So it's just luck I suppose : p
Be real careful with paper towels. Cheap brands will scratch CD's. I've never had a problem using an old t-shirt and water, but then again I make sure all my CD's have a case or sleeve and never get that dirty anyway.
Use a microfiber rag. I have some Monster Cable Screen clean I use on my LCD and the rag doesnt leave scratches. I tried it on a few CD's and worked fine. Glass cleaner works fine too...the important thing is to use something that wont scratch the disc even more. Automotive plastic polish works well on scratches, at least from what I have seen.