Ideally the motor should be run before and after an oil change. I prefer to take it a step further and run it long enough and get it warm enough to burn off cold engine condensation which you WILL have in these temps. This could take 30 minutes or more. If at a dock simply put it in gear at low RPM to seed up the process of warming and burning off the condensation.
#1 Warm engine to sufficiently burn off condensation inside. You don't want any more moisture in the engine than absolutely necessary over the winter.
#2 Change oil & filter.
#3 Close raw water intake and remove intake hose from strainer.
#4 Add a lenght of hose to the strainer long enough to reach into a 5 gallon bucket.
#5 Add 3-4 gallons of engine rated non-toxic antifreeze to the bucket. It's usually labeled -60 or -100, but DO NOT dilute.
#6 Start engine and suck antifreeze through it until hose is empty and making sucking sounds.
#7 Remove impeller
#8 Drain water lift muffler
#9 Remove air box and use saran wrap and an elastic band to seal it off.
#10 Remove wet exhaust hose and do the same.
Most boat yards will skip about half these steps...
Always better to DIY or be there IMHO..