Start by cleaning the mower deck and the air intake screen. You may have already gone over several leaves in your mowing, and mulching leaves can easily get clogged in these screens. So, take the time to clean it out really well. While you are doing that, and things are taken apart, take the time to tighten all the nuts and bolts and to check all belts, filters and safety shields. This is the time of year to repair and treat scratched or chipped metal surfaces, and apply a light coat of engine oil to pivot and wear points to prevent rust. Of course, these are just the things you should do once a year. There are things you should be doing throughout the year to prepare to winterize.

For one, change the oil and the oil filter in your lawn mower. How often you need to change the oil really depends on how often you use it. It is much like a car in this respect. If you have a small yard, changing it once a year is probably enough, so do it when you winterize, and replace the oil and filter at the same time. This needs to happen at the end of the season to ensure that you'll be ready to go next spring. So, the best thing to do is mow your lawn, then drain the old oil while the engine is still warm to get a complete flush and prevent any contaminants from settling back in the oil pan.

During the winter, if your lawn mower sits with fuel in it, and that fuel is left dormant, it will start to decompose. The chemicals begin to interact, varnishing the carburetor and causing hard starting, or no starting of your lawn mower come spring. So, to winterize it you will want to either empty your tank, or add a fuel stabilizer to keep the carburetor from clogging. If you choose to add stabilizer, be sure to run the engine for a minimum of five minutes after it is added so that the stabilizer has a chance to circulate throughout the entire engine.

If you still have your operator's manual, check and see what it has to say about winterization. It might have some suggestions for winter storage, such as checking the battery and the electrolyte levels.

Part of winterization means keeping your mower safe, dry, and covered during the winter, whether it is indoor or out.
Of course once winter is over, you are going to want to bring your mower out of winterization the right way. You'll want to check the tire pressure and all fluid levels to ensure your equipment is ready to go. Be sure that the first time you use it, you run the engine at low to medium idle for a couple of minutes. This gives the oil a chance to be redistributed through the engine.

If you are not up to trying to winterize your lawn mower yourself, or if you are afraid you will do something wrong, don't just leave your lawn mower to get damaged. Instead, take it somewhere. Any John Deere store will have a mechanic who will do it for you.