1) Add layers - That first chill in the air should mean you bring out the fall blankets and get ready for some chilly nights in. These can lower your energy bills later on.
2) Check safety devices - Test all smoke detectors and CO alarms, replace batteries as needed.
3) Inspect the roof and gutters - Leaves will clutter the areas later down the road, but it's a good idea to give everything a quick inspection before this happens. Look for worn seals and pull any sticks or anything blocking your gutters.
4) Clean dryer vents - Pulling lint out can be quite the task, so feel free to hire a professional. It can't hurt to inspect your washer hoses, too. Those can wear out without notice.