In a perfect world, you would only seed in the late Summer, during the months of August or September. In the real world, we recommend that you seed if you have a bare dirt spot. It is always better to seed the area right away, rather than leave it bare.
If your spot is bare dirt, your job is pretty easy. First, use a garden rake or some tool to loosen the soil. We love the Garden Weasel. Next, spread the seed at the recommended rate, and lightly work the seed into the soil. For added benefits, cover the spot with some Compost and work it all in together.
If you have a lot of thatch, or dead grass, on top of the soil, you will need to loosen it up to expose the real dirt you want to seed into, or spread a light layer of real topsoil, not Peat Moss. Spread the seed on the fresh topsoil or freshly prepared ground and lightly work it into the top 1/4 inch of soil. Cover the area with a light layer of Compost or Pelletized Newspaper Mulch.
If you’re adding a fair amount of topsoil, you will be better off seeding in the late Summer or early Fall, as opposed to the Spring or early Summer. The reason for this is that topsoil carries a lot of weed seeds that will sprout better in the Spring and Summer. Keep the area wet for 3-4 weeks to get the grass to sprout and water it a couple times per week until it is fully established.