Indoor (heated if possible) storage is best for guarding against moisture and rust. To prevent flat spots from developing on your tires store the bike on it's center stand with most of the weight off of the wheels. If that's not possible move the motorcycle slightly every month.
Stabilize The Fuel:
Fill the gas tank and add stabilizer to the gas. With fuel injected bikes, run the engine so that fuel stabilizer gets into the injectors. With carburetors, turn off petcock and drain fuel bowls.
Tend To The Battery:
Attach maintenance charger to the battery. If the battery is a non-sealed type, check fluid levels and add distilled water if needed. Avoid using trickle chargers which overcharge batteries in storage.
Lubricate Controls And Other Mechanical Parts:
Lubricate cables and change front fork oil as required by owners manual. Lubricate and/or oil other exterior unsealed moving parts.
Change Engine Oil And Filter:
Old oil can develop acidic qualities and cause corrosion. Change it prior to storage and possibly again in the spring.
Inspect Lubricate Final Drive:
Chains should be cleaned - checked for proper tension and lubrication. Check the oil level on shaft drive bikes and add or replace it as necessary.
Inspect / Service The Cooling System:
For water cooled bikes test the coolant for freeze protection. Look for any signs of rust or leakage. Ensure that the coolant is at the proper level. Drain and flush the coolant every two years.
Inspect And Service The Brakes:
Remove the brake pads and inspect the calipers for corrosion. If left unchecked corroded parts can eventually cause brakes to seize up. Replace faulty parts as necessary.
Inspect/ Replace Tires:
Check the condition of tires, including tread depth. Tires with wear bars showing 3/32 or less of tread remaining, or older than six years should be replaced.
Inspect/Service Electrical System:
Look for any signs of corrosion on exposed electrical connections. A thin coating of silicone dielectric grease can help prevent corrosion.
Be sure to use recommended fluid from a sealed container.
Check Torque Of Threaded Fasteners:
Ensuring that key nuts and bolts (i.e. those that could threaten life or limb if they became loose) are at their proper tightness is especially important.
Clean Protect Surfaces:
Give your bike a thorough cleaning and then polish and wax all painted and chrome surfaces.
Clean and polish aluminum and stainless steel surfaces with the appropriate metal polish.
Inspect/Replace Air Filter:
Inspect the air filter to see if it needs cleaning or replacement.
Clean And Treat Leather:
Use a high quality dressing to treat all leather surfaces.
Treat Cylinder Walls:
To help prevent cylinder wall and piston ring corrosion, remove the spark plugs and add 25cc of motor oil.
Then with the plugs removed use the starter to turn the motor over several times to distribute the oil. Reinstall spark plugs and tighten to the specific torque.
Consult The Owners Manual:
As a final check to make sure that you haven't missed anything, review the maintenance schedule in your owners manual to determine if any other services are required.