How often should I lube my chain?
The correct method to lubricate a chain is "lightly and often," but most cyclists follow that advice by oiling the chain before every ride, which coats the drivetrain and leaves a black, gritty mess where a once-pristine drivetrain once meshed. Unless it rains during your rides, once a week or every 250 miles is more than enough time between chain lubrication intervals. Keeping your drivetrain clean is more important than oiling it regularly, because grit and grime cause more friction and do more damage to your drivetrain than running your chain dry will ever do. Wipe your chain and sprockets clean with a terrycloth towel first and then, using a light-viscosity lubricant like Pro-Link, carefully drop the oil at the gaps between the rollers and the side-plates. Turn the cranks at a moderate rpm so as not to spray oil all over the bike to work the lubricant into the chain's internals and then wipe all of the residual oil from the chain and sprockets. The chain rollers and sideplates should be dry when you are done. Only the inside of the chain's rollers and pins need to be oiled - do this and your bike will stay clean, and your drivetrain will enjoy a long and efficient life.
Looking for more information? Check out these articles:
What things should I do before every Ride?
How to Inflate your Tires
Wheels
Brakes
Bounce Test
Tires