How do I re-sow an existing lawn?

Michael, it's important to de-thatch the lawn first. They make machines that do that, but we've always just used a metal leaf rake. Get all that dead grass out, then when you scatter seed it can reach the soil. Keep it moist and in about 6 weeks you should be able to mower it. One more note, make sure to cut the existing grass fairly short before you sow seed.

Yes, over-seeding is a common practice to thicken up the grass. We've done it by lightly raking lawn, then spreading the seed either by hand or with a seed spreader like this one. If it's just a small area, then I've been able to scatter it by hand easily, but if it's a bit larger area, or the whole yard, you will for sure want a broadcaster like this one. Ideally you will do it before a rainy season set in, or in the fall before snow. (that's the best time here in NW Wisconsin)

We did this at 2 of our previous houses. For the house that just needed

more fuller grass" we tilled the yard first and then used a spreader to go back over and planted the seed. In areas where we had no grass, we planted sod

At the house that we tore all of the grass up and started fresh - we used a seeder to rip it up and then reseeded over top with a spreader. - it was a pain in the butt, but we didn't to use chemicals.