1. Stabilize your fuel
Today's unleaded fuel has a shelf life of 3 to 4 weeks before it starts to break down. Some people say that draining the tank & float is what is needed to help prevent the gas from turning to gunk. My opinion, there is no way to drain every bit of gas, mainly from all the small spaces & including the jets in the carburetor.
I use the recommended amount of fuel stabilizer to a full tank of fuel, then run the engine for at least 15 minutes to get the stabilized fuel all inside the engine. This will help the left over fuel from oxidizing and turning into varnish.
2. Change the oil
Perfect time to change the oil since the bike is nice and warmed up. Residual fuel in the oil can oxidize from sitting in storage. Changing your oil now will remove all the sludge and dirt that would begin to deteriorate. Not to mention, changing oil now guarantees fresh lubrication when its time get your ride back out again. I use synthetic oil (don't be cheap, its your bike after all) which will hold up far longer into next year's riding season then regular oil. And don't forget the engine a few minutes to disburse the oil all through the engine.
3. Prepare your Battery
Batteries should be kept under a constant charge in order to prolong their life. Attach a Battery Tender or a special charger that doesn't overcharge the battery. A trickle charger can be used but it must not be run for any more than a 30 minutes each day. if you only have this type, get a appliance timer for a few dollars. If your bike is going to be stored in a freezing climate, remove the battery completely out of the bike and put it in a warm dry place. Either way, the battery should be kept on charge.
4. Clean and Lube
Any type of road dirt or sand will help corrode any metal surface when its in storage. Spend the time and give your bike a good cleaning before putting it to sleep for the winter. Lubricate the chain and all other moving parts including cables. Use a metal protecting spray on the underside of the frame and drive train. This will stop any rust on areas exposed from pitting or scratches from normal riding.
Never use WD-40 on your Harley, ever. its not made for the harley. talk with your local bike shop, they'll have a list of product to use that safe for your harley.
5. Check your Tires
Make sure your tires the correct amount of air. If you can using an air compressor, deflate your tires to get rid of any moisture that may be in the tires.?then fill them back up with clean compressed air. Remember to do this step again before riding in the spring.
If you can, lift your Harley so the tires are not under load. This is especially smart to do if the bike will be stored in freezing climates. Make sure your bike is secure, this is extremely important. Motorcycle lifts with the bottle jacks are not a smart idea to use for long periods of tim, they can fail.
6. Cover your Harley
Inside or out side, your bike should be covered all the time while winterized. Use a cover that can breath & please do not use those plastic tarps. Any type of moisture should be prevented, it can become trapped under the cover on your bike's metal surfaces. Be sure to cover your exhaust pipes end to keep anything from making a winter home inside them. And last use a plastic shopping bag over the carbs intake. This will insure that no moisture will get in while the bike is resting.
That's basically all there is to know about storing your bike. Just remember when the bike is stored, resist the temptation of periodically starting the engine, this will not help in any way.
When your ready, drain the stabilized fuel and start riding again.