A good fall cleanup is the best thing you can do for next spring's lawn and garden.
Keep leaves off the lawn. A thick layer smothers grass and invites snow mould, so mow lighter layers into mulch and rake or blow the rest into beds or the compost pile.
Cut back perennials that tend to rot, such as hostas and daylilies, but leave seed heads on coneflowers and grasses for birds and winter interest.
Finish with a last mow at around 3 inches, a fall feeding for the lawn, a fresh layer of mulch on beds and a blow-out of the irrigation lines before the first hard freeze.