As qquake2K and several others have said, Baby Wipes are MAGIC when used immediately following the flight.
I usually go one step further and coat the interior of the motor case with Superlube during the Aerotech reload assembly process. This is has never failed me yet. I'm able to pretty much totally clean the cases immediately following the the flight using paper towels and Baby Wipes as needed. I bring a Home Depot bucket to launches for use as a trash can. Clean as you go.
There have been occasions when I have failed to clean a case in a timely manner. I have a large collection of gun cleaning supplies and almost all of them work to different degrees. Ballistol is pretty good stuff...expensive...but I've used pretty much all the CLP products, too. My standard procedure for caked-on deposits is to soak overnight in hot water and Dawn dish soap. A dedicated bottle brush, plastic dish basin, a couple of old toothbrushes, paper towels, and a final wipe down with Ballistol generally does the trick. Stubborn exhaust deposits on rear closures sometimes require a longer (days) soak in CLP but that all depends on what you think is "clean enough". Most of my hardware is hard to find Dr. Rockets so I try to take good care of it. YMMV.