Just make sure and tilt the motor all the way down and let all the water drain out so if it freezes it won't damage your motor. Fuel treatment for water and ethanol. Make sure the drain plug is out of the boat and you should be good.
This....also pull the kill switch and crank it over a few times with the motor down to allow the water pump to push water out of it. Do not run it out of the water...you'll fry that water pump pretty quickly.
Now is also a good time to change your lower unit grease just to make sure there isn't any water in it that could freeze.