Fill 'Er Up - And Don't Forget The Fuel Stabilizer
You needn't bother to drain your gas tank, as some will recommend. Instead, ride down to your gas station, fill your tank and add the prescribed amount of Sta-Bil fuel stabilizer. Gasoline will eventually degrade and turn gunky, and that gunk will mess up your fuel system. The Sta-Bil will mix and run through the fuel system on your ride home. And when you get home, the engine will be warm, so you can then...
Change Your Oil and Check Your Fluids
No explanation needed here: you'll have fresh oil and a new filter when you're ready to roll come springtime. And it goes without saying that if your coolant levels are low, add anti-freeze - not water. Once you're done, start the bike up again - this will circulate the oil through the engine and provide additional protection against corrosion. Now, there's some discussion about removing the spark plugs and squirting some oil down into the cylinders. We're going to say that if you're storing your bike for less than six months, this isn't a necessary step.
Remove and Store Your Battery
We'll also recommend that you pick up a battery tender; you'll want to remove and store your battery in a clean, dry place, but you also want to be sure it keeps a charge over the winter. Charging it once a month should suffice.
Protect Your Tires
You'll want to keep your tires in good shape; they can develop flat spots or even absorb moisture from your garage floor. If your bike has a center stand, use it and not the kickstand; if you have front and rear motorcycle stands, even better. If you don't have any of those, putting plywood or pieces of carpet under the tires can help prevent moisture damage.
Put It Away Clean
Giving your bike a thorough wash before garaging it will not only ensure that it looks good when you take it out next year, it'll help keep the finish from corroding. Make sure that you dry your bike thoroughly; once that's done, wax the painted surfaces and apply a light coat of WD-40 to any other metal surfaces. (Be careful not to get that WD-40 on your windshield or brake discs or pads.) This will help protect the bike from corrosion. If your bike has a chain drive, it's a good idea to clean, adjust and lube the chain. If you don't have a good motorcycle cover for your bike, it's a good idea to invest in one.