To overseed your lawn, you need to dethatch, aerate, amend the soil, mow your lawn low, spread seeds evenly, and apply starter fertilizer.
This second method of overseeding is also effective, if you’re unable to use a slit-seeder. Aerate several times before broadcasting seed; aeration holes should be spaced not more than 2-3 inches apart. Use core-type aerating tines that remove soil plugs for better seed-to-soil contact. ...
If you use your lawn a lot for parties or if you have kids and pets, then you will likely need to overseed your lawn more often;expect to overseed your lawn once a year. Foot traffic wears down grass over time, so the more you use your lawn, the more damage your grass will have...
To overseed your lawn, you need to dethatch, aerate, amend the soil, mow your lawn low, spread seeds evenly, and apply starter fertilizer.