How to Winterize and Maintain Your Mower
Time to take care of your lawnmower for winter. Most of the leaves have fallen, irrigation systems have dried up and been blown out, and there's not much yard work left to be done as we await the first snowfall to land. Now is the ideal time to give your dependable mower some tender loving care to ensure it stays dependable when called into action again next spring.
Drain or stabilize fuel.
Turn your fuel valve off and then start your mower until it stops. Doing this will ensure that there's no fuel left sitting in your carburetor over the winter months. Add fuel stabilizer to the tank to ensure the remaining gas does not go bad over while the mower sits idly in your shed or shop. Always read and follow all manufacturer instructions when putting additives in your fuel.

Fuel Valve Open

Fuel Valve Shut
Keep a clean machine.
Now is the time to give your mower a good scrubbing and hose down to remove a season's worth of debris and built up clippings. It may be necessary to use something like a putty knife to scrape dry, harder clumps of grass. For a push mower, just tilt the mower straight back and find something to weigh the handles down then give the underside of the mower a good spray down with a garden hose.

Keep a sharp blade.
Now that you're done with the mower until spring, sharpen the blade to ensure a clean, even cut next year. There's a multitude of video tutorials online for all sorts of mowers showing how you can do this yourself. Or you can take your mower down to the local lawn and garden center and they'll do it for you (for a fee).
Paint job.
Hit any scrapes that have developed from use with a bit of touch up paint. This prevents rusting.
Remove battery.
Though not always necessary, it's often recommended by manufacturers to disconnect and remove the battery from your mower for safe storage in a dry location.
Get greasy.
Choke and throttle linkages need to be cleaned up and hit with some spray lubricant. Hit fittings on your mower with a touch of grease.
Check for deals on a new mower.
Mowers tend to move out of showroom floors much slower in the off season, so you may be able to find a good deal if you are in the market for an upgrade. New models may be coming in for the next season and when that happens you can often find a good deal on the older models. Add in sales around the holiday and you just might get lucky.

Winter Hibernation
Keeping your mower well maintained and in good condition will have you ready for next spring when it's time to pull it out of the shed and yank on that pull starter again. Now you know what to do, go forth and own your yard.