If you did not fertilize in summer, you can still use a lawn food plus iron in September, then a winterizer in October or early November. Do not mow it shorter for winter. Mowing it very short makes your lawn more susceptible to winter dessication and stress. Grass needs less water in the fall, but water should be applied during dry spells. Don't drain your sprinkler system until necessary and buy a manual sprinkler for those times after your system as been drained.
Autumn is also a good time to take care of other lawn problems.
It is a good time to seed or sod a lawn while air temperatures are cool and soil temperatures are warm. Fall core aeration leads to better moisture penetration and thatch reduction. An application of a pre-emergent herbicide at this time of year is effective for control of annual bluegrass. Post-emergent herbicides control perennial weeds very well in the fall.