Any maintenance schedule will vary depending on how much you ride and how hard you ride. The following information is intended for cyclists who ride just about every day. If you only ride once a month, you certainly don't need to check your bike every week. But to keep your bike in the best possible condition, try to stick as closely as possible (and practical) to the schedule.
Things to do every week.
Clean your bike completely—particularly lights, reflectors, and wheels—with a damp rag.
Check reflectors and lights for cracks, and check the batteries on your lights and computer.
Things to do every month.
Check the bike's lubrication. If necessary, lubricate the chain, cables, and pivot points (on brake levers, shift levers, brake arms, and derailleurs) with a recommended lubricant.
Check that all nuts and bolts are secure.
Check that all the joints housing ball bearings are secure.
Check all spokes closely for tightness.
Things to do every three to six months, as necessary.
Clean the bike thoroughly and wax the frame finish.
Clean the chain, sprockets, and derailleurs completely and relubricate.
Have your wheels trued if you ride off-road a lot (otherwise only when needed).
Replace brake pads if worn and readjust brakes.
Test gear shifting and readjust derailleur cables if necessary.
Closely inspect tires, remove any debris lodged in the tread, and replace tires if they are cracked or badly worn.
Clean and lubricate the tubes of your suspension forks, and replace any worn parts or seals.
Things to do once a year.
Take your bike into the shop for a tune-up. (Even if you're an expert mechanic, it's always good to get a second opinion. Another mechanic may notice something you missed.)
Overhaul all component systems. Remove all ball bearings; clean them, repack them, and relubricate. Unless you are experienced in bicycle maintenance, this should be done at a bike shop by an experienced bike mechanic.
Remove the seat post and relubricate it (be sure to mark the seat post height so you can reinstall it correctly).
Remove the stem and relubricate it (be sure to mark it so you can reinstall it to the correct height).
Clean the cable and replace it if it is at all frayed or damaged.
Check the pedals for damaged teeth and grinding bearings. Replace or repair pedals if necessary.
Replace the tire patches and spare tube you carry in your repair kit if you haven't used them all year.
Unload your bike's tool bag and home tool box to check that all tools and equipment are in good condition.
If you have suspension shocks and use them frequently, take your bike in to a bike shop for a suspension check (include it in your yearly tune-up).
Your bike should be thoroughly cleaned on a regular basis—either every week or every few months depending on your riding habits. If you ride off-road, chances are good your bike will get dirty quite frequently. You may need to wash your bike after every ride. More than following any particular time-table, it's important to clean your bike as often as necessary—and as soon after it gets dirty as possible (before the dirt dries and hardens). A grinding sound or feel in any of the bearing joints will indicate dirt is stuck inside and an overhaul is needed. Clean bikes look better, but, more importantly, they're safer. A buildup of dirt and other particles can quickly affect the performance of the brakes, chain, and other components.
To clean your bike, first get it completely wet with a sponge or low pressure water hose (don't wipe dried dirt off the bike because you could scratch the finish). Then get a bucket of soapy water and a soft rag to further scrub the bike and wash away any dirt or grime from the frame and wheels. To wash the wheels, start at the hub and axle and work your way outward by wiping the spokes and rims. Do not use an oily cleaning product on the rims or the rim brakes will become ineffective. Remove any dirt, tar, or stones lodged in the treads. When you've finished, rinse all dirt and soap away completely.
The most important part of the bike to keep clean is the drivetrain. Dirt or particles that get into the chain or bottom bracket can grind and wear down the parts. Short of disassembling the drivetrain and cleaning the parts individually, you can wash the area thoroughly with a brush and water or with special chain cleaning equipment available at bike shops. Loosen any debris from the chainwheels, pedals, cranks, and derailleurs. Avoid spraying water directly into areas where there are ball bearings, though.
To clean the chain, spray or wipe it with degreaser, then run the chain through a wet, soapy rag (or chain-cleaning device) until all the oil and grease is removed. A good method to do this is to hold the rag around one part of the chain, then turn the cranks backwards to pull the chain through the rag. Once the chain is clean, relubricate it with a light coating of a recommended lubricant, and run a dry rag over the chain to remove excess lubrication.
After cleaning, inspect your bike closely to make sure all the parts are clean and working properly. Allow your bike to dry completely before you ride it.