Hello. Here are the basic steps, along with info about winterizing the rest of the boat:
1. Add a fuel stabilizer / preservative such as Bombardier's "2+4" or Stabil proportionately to the fuel tank, along with a fuel injector cleaner .
2. Change the water separator filter if you have one, filling it with fresh, treated fuel before installing it.
3. Grease all steering and tilt pivots. Make sure the ram is wiped clean, then coat it with a lightweight grease.
4. Hook up a flush attachment (e.g., "bunny ears") to the engine and run the engine at a low idle for about 10 minutes, making sure the thermostats cycle open. I would actually run at idle for half an hour to get the treated fuel into the engine, then shut the engine off. Allow the water to drain - optionally you can run antifreeze in through the bunny ears, but it should not be necessary.
5. Change the oil while the engine is warm (not hot).
6. Drain the gearcase and refill it (from the bottom until oil comes out the top hole to avoid air pockets) with the appropriate lube. When you replace the drain screws, make sure each has a gasket or o-ring.
7. Leave the engine trimmed all the way down so any water remaining will drain. Put something down to catch any drips, and note that this is a good chance to find any gear oil leaks, since an exhaust will normally drip black, and an oil leak will be the color of whatever you put into the gearcase.
8. If you have a fresh water system, livewell, etc. run all the water out of the system, then disconnect the inbound hoses to the pumps, run a hose from the pump to a container of non-toxic antifreeze, then turn the pump on until antifreeze run out. Don't forget to replace any lines you removed. For the fresh water system, the antifreeze can be added directly to the water tank. Be sure to drain and bypass the hot water heater if you have one, otherwise you'll need 6 gallons of antifreeze just for that.
9. If your boat is stored in a heated area, leave the batteries on the boat. Otherwise remove the batteries and put them in a cool, dry room. Charge them the week before you're ready to launch the boat in the spring.
10. If the boat is on a trailer, jack it up and put blocks under the axles and trailer tongue. Make sure the wheels spin freely and smoothly, then grease the bearings and rotate the wheels again.