Depends on whether you're storing the boat indoors or outside. If you're storing the boat outside, then taking the mast down is a good idea, so you can shrink wrap the hull properly.
Winterize the engine:
Change oil, impeller, flush cooling system, fill with antifreeze, fog engine,
Winterize the fresh water system:
fill with appropriate non-toxic antifreeze and work the antifreeze through the various pumps
and hoses and through hulls.
Work and lubricate all the through-hull seacocks.
Empty and dry the bilge.
Shrink wrap hull with ventilation.
Electrical System Winterization:
Remove batteries, and store in a warm dry location, like your basement.
Check charge level and use "float charger" to maintain battery level.
Inspect electrolyte levels monthly and top off as needed.
Remove all "portable" electronics from boat and store in warm dry location.
YMMV, and this is just a very rough guide to what you need to do. It will vary depending on what kind of boat you have, what systems are on the boat (pressure water, hot water, etc) and where you will be storing it.