Some links for you for reference:
Howstuffworks "How to Winterize an Outboard Motor"
Winterizing Outboard Motor on the Trailer
Winterizing Tips/Technical Information/Sales&Service/Tohatsu Outboard Motors
Boat Winterizing by David Estensen
Couple things I'll add are, if you can, put a cover on the motor or at least the cowling (keeps rodents/birds/etc.. from nesting up in the cowling.
Definately drain the lower unit oil, cause if any water is in the lower unit oil and it freezes,, can crack the LU housing.. dont wait till spring to change.
If you have a water system (fresh water washdown), put some RV pink anti freeze in the system then run the system until pink water comes out.. that way you wont bust a pump and it will keep the water (residual) from freezing. Same thing for macerator system pour in some pink RV anti freeze so water wont freeze up and bust the pump(s)
Top off fluids to prevent any condesation. Hydraulic steering, compass oil (if needed), fuel, oil tank(s).
DEFINATELY ADD STABIL or some fuel treatment!!!!! very important!!!
Will prevent fuel from going stale and will prevent varnashing and gumming of fuel system. Once you "un-winterize" then change out all your filters (fuel/oil)
Get out as much residual moisture/water as possible then if you have a cover, cover up the boat and let'r sit till spring.
Things over looked:
Trailer maintenance, should you have any water (residual) in the hubs or bearings.. could force the protective caps out if the water freezes... best to lube up the hubs prior to letting the trailer rest.
Maintain tire pressures just as you would if you were using the boat
if possible, jack up the trailer to releive the pressure off the tires (so you wont get flat spots on the tire itself) and remove the tires (good theft preventative measure as well.
If you can, cover the tires to prevent uv damage while trailer is at rest.
Good time to go over wiring and any repairs/bulb replacements you might need to do. Sometimes water will get into connections and bulb sockets... so I like to at least pull the bulbs and coat the contacts and bulb contact ends with die-electric grease and re-install. Prevents water build up and prevents corrosion!
lastly, remove ALL gear from the boat - life jackets, safety kits, equipment... nothing worse than gear sittin in wet/damp closed deck locker, leave all hatches partially open to allow for air to circulate