It’s likely been a while since you’ve looked at your roof, so the first step in getting it ready for winter is to grab a ladder and check it out.
How does it look? Any missing shingles (some sides of your roof are hard to see from the ground, so get all areas checked)? Any exaggerated sag in the roof ridge line? Any other damage from nearby or fallen trees/branches? If so, you should arrange for repairs before winter sets in – before those damaged areas are concealed by snow, and your home’s interior is at risk of water entry.
Check out the gutters as well, and clear out any accumulated leaves and debris. Once you’ve cleaned out all the stuff, give the gutter a quick flush with a garden hose to make sure there is free flow through the downspouts as well.
It’s also important to check the attic. Make sure you have a good amount of evenly distributed insulation (ensure it’s not blocking any roof vents, especially near the edges of the attic, where the soffits are). Adequate insulation helps keep your home’s warm air in the home where you need it, and not wafting up under your shingles where it can be a factor in the formation of roof ice dams.