While mashing the pedals on my mountain bike several years ago my chain broke. I learned the hard way the importance of keeping the transmission of your bike clean. It is very dangerous to have a chain break in the middle of climbing up a hill. I was lucky not to have a serious injury. Lubing your chain regularly can keep things running smoothly and prevent things from breaking down. I now clean my bike, cassette, chain, derailleur, religiously.
I found a great product from Finish Line that helped me clean my cassette easily and thoroughly, it's Gear Floss Microfiber Rope: http://www.finishlineusa.com/products/gear-floss.htm. It looks like pieces of a basketball net but works really well. In fact, I've been using Finish Line products for years.
While de-greasing one day, I wanted to see how clean my cassette was getting. I ran the gear floss through the cassette and was pleased to see my cassette is actually chrome and not gun metal black. I was shocked. Even after doing the de-greaser it still collected more grease. So I grabbed an old shoe lace and a small cord that I had on my work bench to see if they did the same job of sucking all the grease and dirt out. The shoe lace only got the surface grease and oil and the cord pushed things around but did not absorb any material substance. I then ran the gear floss through again and it came out with chunks of material that were not coming out with the shoe lace or the cord.
The Gear Floss is easy to use without removing your back tire and allows access to the tightest spots in the derailleur. It is also easy to use while still mounted on your trainer. When I am done with my cleaning I now put a fresh coat of Ceramic Wet Lube from Finish Line on my chain. Check it out: http://www.finishlineusa.com/products/ceramic_wet_lube.htm This lube is long lasting and creates a special coating on the chain to give excellent drive train efficiency.