Winterizing your boat is a mostly common sense procedure. The things you are seeking to protect are often costly and can be badly damaged or destroyed by freezing conditions or even lack of use.
Some items for your consideration:
Fuel Systems: One of the most common problems with spring startup is bad fuel. To help with this, use "STABIL" or another fuel preservative in the tanks according to the proper mix. In other words, If there is 1/4 tank in a 100 gallon tank that means you need enough Stabil for 25 gallons. Rock the boat to help distribute the Stabil in the fuel and then run the boat for ten to fifteen minuets, until the engine reaches normal operating temperature.
While the engine is running: use a little belt lubricant in the alternator drive belts.
Use fogging oil SPAREINGLY on the carburetor and linkages. DO NOT OVERUSE, It should coat the items, but NOT DRIP.
Steering and outdrive Lubricate as necessary any steering cables. Use Manufacturer Approved Lubricant on steering cables and hardware.
Use Approved lubricant on outdrive zirc fittings. Change lower unit oil. Pull prop and grease shaft. Store prop in a secure location.
Lower outdrive & trim to lowest position to retract the hydraulics fully. This is also a good time to change out all your zincs.
Batteries If your boat will remain in the water, check the batteries and make sure the date is good throughout the winter. Make sure they are full of electrolyte. Clean the terminals and connections. Make sure your battery charger is working properly. Spray terminals with no-cro or other anti corrosive. If your boat will be in dry storage, remove the batteries and place them on a trickle charger.
Sanitation Systems. Drain and properly dispose of waste. Clean toilet, then Flush system with clear water 2 times, and drain the entire system, including hoses and pumps completely. Do not allow water to remain in pumps, lines or hoses.
Fresh Water Supply Drain completely, refill with fresh potable water and add 1 tablespoon of bleach per 5 gallons. Allow to stand for 1 hour and pump out through rear most faucet. Check toilet and bail out if it refilled. Empty grey water sump and dry completely. Use a sponge if necessary. Do not allow grey water to stand or it will smell up your boat for weeks.
Cabin inspect cabin for any food or drink. Check reefer and remove all food and ice trays. Allow to defrost with door open. Dry thoroughly. Allow door to remain open during storage period.
If you find any cold beer, consume it immediately.
Do not allow any foodstuffs to remain aboard. It will draw "critters". Clean stove. Clean dish sink and microwave. Remove bedding and towels for washing and storage. Spray liberally with a mold and bacteria killing aerosol such as Lysol Spray Disinfectant, especially bottom sides of cushions and upholstery. Also spray enclosed storage spaces.
Make sure air-conditioning is off and the drain pan dry. Make sure all electrical power is off, except, for bilge pumps and engine room heater . Leave a single 100 watt bulb burning to disperse humidity and prevent freezing. If you are dry storing you may not be able to keep a bulb on. Therefore, you must make certain there are no fluids abord which can freeze.
Electronics Remove any electronic devices, clean housings with windex applied lightly to a soft cloth. Use a windex moistened q-tip to clean any connections. Treat antenna connectors with silicone and place a plastic baggie over the ends. Seal with electrical tape or duck tape.
Store individual units in plastic bags.
Canvas and deck Clean deck, seats and canvas with a good disinfectant solution such as Lysol or Pine Sol. After the canvas, deck and seats are clean, wash again with a mild solution of the same soap and allow to air dry. DO NOT RINSE. Make sure canvas is dry before stowing. Polish chrome or stainless deck fittings and rails with a good, silicone based chrome polish. Do not leave polish on the fittings as it is difficult to remove after it has dried for an extended time.
Cover The boat with a good grade of poly canvas. Usually the silver is a better grade then the blue. Tie it down using bungee cords. IMPORTANT Make sure there is an area both stern and bow where air can get in and allow the boat to breathe.