Definitely use the highest % isopropyl alcohol you can find. Don't use denatured alcohol, rubbing alcohol, or windex.
Pick up one of those security screw bits - you'll need to open your system sooner or later.
Goo Gone or any kind of alcohol both work well for cleaning the outside of systems and taking grime off controllers. Goo Gone is also a must for removing the ubiquitous sticker residue from retro games.
Run a CD-lens cleaner CD through your Duo once in a while.
Is the spindle noisy? Put a drop or two of sewing machine oil down the shaft. Also put a drop or two on the gears if you have cause to open the system up.
Keep some Radio Shack electronics cleaner and Q-tips around to clean leaky capacitor gunk off boards, dull solder points, and the insides of grungy controllers. People talk about running their systems through dishwashers, but I avoid this and clean the insides by hand. Dishwashers may be OK if you dry it out completely, but I've seen rainwater oxidize exterior copper plating on a number of fancy buildings very quickly and I've also seen a corroded Turbostick board ruined by exposure to moisture.
Most importantly, keep your system covered with a cloth to keep the dust off when not in use!