Fall is a great time to renovate thin or poor quality lawns.
Renovation is the last step before replacement. Use this method for lawns that are thin, have lots of bare spots or are full of weeds.
Start by removing the thatch layer if it is greater than ½ inch thick. Use a vertical mower, known as a dethatching machine, on actively growing lawns to cut through the thatch layer and insure seed-to-soil contact. Rake and compost the thatch.
Or use a core aerator to remove plugs of soil and thatch, relieve soil compaction, break through the thatch layer, and provide good seed-to-soil contact.
Spread grass seed over the renovated area using a broadcast or drop type spreader.
Continue to mow and water the lawn as needed. And wait a month before fertilizing the lawn with a low nitrogen slow release fertilizer.
A bit more information: Consider renting a slit seeder if thatch is not a problem. This machine cuts slits into the ground and drops the seeds in place, insuring good seed-to-soil contact for better seed germination