The one thing that I always, always do after every ride, is wipe the bike down, and rub some Bike Lust (a silicone spray that offers some protection to road grime, which is very acidic) on it. I do that not just to keep the bike clean, but also because it gets me up close and personal, so I can really see if anything is wrong. Outside of that, I check to make sure the important bolts and other fasteners are tight, that the brakes are working properly, the headset isn't too loose, and the tire pressure is where it's supposed to be.