Upgrade the condition of your soil this time of year by adding a layer of humus or organic matter. You can achieve this easily by leaving a layer of mulched leaves to decompose. Also, consider without debate an aeration of the lawn. This is typically only needed every three years but most of your better golf courses do this annually. And that should be enough persuasion.
Immediately after your aerating is done you have an ideal opportunity to overseed. A high quality seed "blend" is recommended over a "mix." This is discussed with greater detail here on The Best Lawn Grass. A high quality blend will give you grass that is more resistant to pests and disease as well as extreme weather conditions.
Fall is also the best time to add some lime to your lawn's soil. Most lawns are naturally acidic and a routine treatment with lime will keep the Ph in a safe range of 6.0 - 7.2. Soil that is too acidic or alkalinized can be difficult for beneficial insects to live happily.Lime also adds much needed calcium and magnesium and enhances the soil structure which will benefit grass seed germination.
Essentially there is much to do in the fall. But if these things get accomplished this translates into less mowing, less watering, less pest and weed controlling in the following growing season.