Before planting grass seed it is a good idea to consider how you intend to water the lawn. It is possible to use a sprinkler head, attached to a hose, to water the area. But, if you intend to add an underground sprinkler system, which may or may not be hooked to automatic controls, you will want to install the irrigation before moving onto preparing the soil and planting the grass seeds.
Grade the area where you intend to plant the grass seed, so that it has good drainage. You don't want water standing in puddles on the grass seed or lawn after a rainfall or watering.
Till the topsoil using a rotary tiller, to a depth of 4 to 6 inches. Remove any large rocks.
Take a soil sample to your local gardening center for testing, to help you determine the appropriate amendments and fertilizer needed, considering your soil type.
Amend the topsoil so that the top 6 inches are about one-third organic matter. Fertilizer (to provide nutrients) will also need to be added. Choose the type of organic matter and fertilizer which will make up for any deficiencies indicated in the soil test. You will want to increase the nitrogen, to double the amount normally used, to compensate for the initial loss of nitrogen caused by the organic matter's decomposition.
Till the topsoil, amendments and fertilizer in a crisscross pattern, using a rotary tiller. The top soil should be well blended for about 5 to 6 inches deep.
Roll the surface of the ground to compact, in a crisscross pattern. If you can walk through the area and just leave a slight indentation with your shoe, then you are ready for the next step. If the area is too fluffy to roll, water lightly and then roll after the soil settles.
Rake lightly, to remove any rocks.
Drag a heavy wooden ladder, which has ropes tied to each end, across the soil to level out any bumps.
Rake lightly, loosening the top quarter inch of soil.
Sow the seeds lightly over the area by hand, using a sweeping motion. The seeds should be released from a hollow fist. Sow half the seeds in one direction and the remainder at a right angle to the first batch--or use a seed spreader. The amount of seeds to spread will vary, depending on seed type.
Drag an inverted leaf rake over the seeded area, applying slight pressure.
Cover the area with mulch. Straw (not hay) can be used, with one bale for each 1,000 square feet. Keep between 3 to 4 straws deep of mulch.
Sprinkle lightly with water.