This is my first winter and I don't have a shop, only an unheated garage, and the tools that came with my bike (and maybe a couple in my house somewhere). What is the bare minimum I should do to prepare my bike for the off-season?
If you live in the frozen north like me, temperatures are already dropping, and before long there will be snow on the ground. Some hardcore riders don't care and keep riding year-round. We don't recommend it, but if you're one of those, I salute you (I used to be, but I don't have to prove how hard I am anymore -JM). That's not me. I don't like the cold, so I put my bikes away while the snow is on the ground and the bike-eating salt is on the road.
A Place For Your Stuff
The first thing you need to think about is where you're going to park your bike for its winter slumber. If you have room in your garage, problem solved. I used to but don't anymore, so I slide it into a self-storage unit close to home. If you choose this option, make sure the facility you choose allows you to store vehicles in their units. Mine does, though they require the battery to be removed. Also, keep in mind that your motorcycle alone may not be enough to trigger the automatic gate to exit the facility in the spring. Ask me how I know.
Other options include motorcycle shops that store bikes over winter. Sometimes you can get a deal on a few months of storage that will include an oil change in the spring. This could be well worth it.
If you must park outside, get a good cover to put over the bike. Be sure to clear snow off the cover soon after it piles up, or even the best cover may tear open under the weight. It's better than nothing, but certainly the last resort.
Once you have a place to put your bike, you can put it to sleep properly. Fill up your gas tank, pour in some fuel stabilizer, and run it for a while. A ride is best, especially for carbureted bikes to make sure it works its way into all of the jets and ports as you use them.
Some people say to change the oil before you park it for winter. Others say to change it right before you get back on in the spring. Still others say just stick with your regular oil change interval. I tend to be in this third camp. That said, my KLR 650 is about due for an oil change anyway, so I'll do it either right before or after it goes in or out of storage for this winter.
If you have a water-cooled bike, make sure your coolant is fresh and topped off, especially if you're not parking in a heated area. You'll be relying on your antifreeze to prevent engine damage during winter's cold temperatures.
Some say you should wash your bike before storing it. (Don't run it through a car wash like this guy.) The argument is that moisture, bacteria, and other nasties that can seriously impact your motorcycle over the course of a winter. Since I ride a KLR 650, washing the bike is against my religion, so personally, I don't bother. I would consider it if my very last ride took me through some deep mud puddles, and I didn't want that glop all over everything else in my storage unit.
You'll want to keep your battery out of the cold and on a trickle charger through the winter months. If you're parking in your garage, this is as simple as plugging in a battery tender and forgetting it. My storage facility requires batteries to be removed, and since it's unheated I'd want to take it home with me anyway. Once I get the bike there, I pull the battery, take it home, and put it on a charger for the next few months. If your bike will be outside, definitely bring the battery in where it's warm. Little will kill a battery more than the cold.
Some people think it's a good idea to lift the bike high enough so that the tires are off the ground. The theory is this will prevent flat spots where the tires are touching the ground for several months without moving. If you run particularly soft tires, such as for track days, this is probably a wise idea. My dual-sport tires are pretty hard, so personally, I don't bother.
Finally, take one last good look at your bike before you tell it goodbye for the next few months and shut the door. It's sad, but it's the price we pay for living in the frozen north.