Here's some in-depth suggestions I picked up years ago:
Winter storage guidelines
Stabilize your fuel and top off your fuel tank
Use a fuel stabilizer product to keep the fuel from going stale during storage. Filling the tank to the top will keep the walls of the tank covered and protected from corrosion. The less air space in the tank the better. Remember to treat both fuel tanks if you have split tanks.
Change the oil and filter
Oil becomes acidic in use and does absorb moisture to a limited degree. Leaving acidic, moisture laden oil in your engine can promote corrosion of internal engine components, as well as sludge formation in passages and low lying areas in the engine and tank. Replacing the oil and circulating it by taking a final ten mile or so ride to fully warm it up will protect everything below the pistons.
Fog the motor
Upon returning from the last ride of the season, let the engine idle while removing the air cleaner and cover. Using an aerosol fogging oil, spray the oil down the throat of the carburetor while opening the throttle enough to keep it running. Once you see smoke at the mufflers, close the throttle and continue to spray while the engine dies. This coats the ports, valves, and guides with a preservative coating of oil.
Remove the spark plugs and give a shot of fogging oil in each cylinder. Reinstall the plugs and crank the engine a few revolutions to distribute the oil on the cylinder walls, and combustion chamber.
Drain the carburetor (extended storage)
Fuel left in the carburetor will evaporate, and can leave deposits in the jets and float bowl which can cause great heartache in the spring. Close the petcock valve and open the drain screw, plug, or bolt depending on the carb you have. If you have a CV carb without a drain screw, I recommend turning off the petcock while fogging the motor to use up the fuel in the carburetor.
Remove the battery
Remove and clean the battery. Grime and acid on the outside of the battery will provide a path for current to travel and allow the battery to discharge. Find a cool dry place to store your battery. Batteries will typically self-discharge internally about one percent a day. You can either charge the battery once a month, or use a smart tender to maintain it until the spring. Keeping the battery charged will minimize sulfating, i.e. corrosion buildup on the plates. Sulfating results in excess battery resistance and ultimately battery failure.
Storage location
Store the bike in a shed or a garage. A moisture barrier between the bike and the floor is a good idea. Lay down a sheet of plastic and a layer of plywood on top of that, and park the bike on the plywood. If you have a lift, store the bike with the wheels off the floor. This will take the load off your suspension and prevent the tires from developing a flat spot. (Don't panic if you don't have a lift, flat spots will work themselves out in a few miles anyway) If you cover the bike, ensure the cover can breathe and not trap moisture. Do not store your bike near anything edible like pet food or bird seed, etc. Check the area around your bike periodically for evidence of rodent activity. A wad of steel wool in the end of the exhaust pipe will keep the critters out. They really like electra-glide fairings for nesting too.
Spring Revival
Check the battery one last time and reinstall it. Route the vent hose carefully and make sure it isn't pinched or blocked, or under the battery. Look for puddles. Check the oil level, but don't add any oil until it's been run, and the oil has been circulated. Check your other fluid levels as well. Check your tire pressures and all your lights and switches before venturing out. After your first ride, install a new set of spark plugs.
If you have a bike where the oil tank is above the engine, i.e. softails, sportsters, FXR's. 1992 or earlier baggers, be forewarned that there is a possibility that a large amount of your oil has found it's way down into the crankcase. Upon starting the engine, the quantity of oil to be returned to the tank can overwhelm the oil pump and some oil may be discharged through the breather. This is a temporary condition and is no real cause for concern. This is less prominent in engines that breathe through the cylinder heads (1993 and newer). I recommend disconnecting the breather from the air cleaner box and diverting it to a can or drain pan when starting the engine for the first time.
