Prepare the ground for grass seed in summer. This is the best time to get perennial weeds out before they reseed, and your seed will have the most chance of success in the wetter autumn months, without the summer foot traffic.
Walk slowly over the lawn site to look for and remove any large stones, plant debris and trash. Dig up large stones with a shovel, or break them up with a mechanical or hand-operated stone breaker.
Get rid of the weeds. Perennial weeds such as dock, nettles and brambles need to be dug out by their tap roots to keep them from coming back the next year. If the ground is so covered with weeds that it's not practical to remove them by hand, consider laying a plastic cover over them for two months to kill them in the sun, or spray the area with an herbicide.
Take the weeds away from the lawn and dispose of them in a plastic bag, or put them in a burn pile. Do not add them to a compost heap as they could reseed.
Make the soil surface as smooth as possible. Remove any existing topsoil and set it aside to avoid mixing topsoil and subsoil. Dig up the subsoil with a tiller or a shovel to loosen it. Move the subsoil to get rid of any hills or holes. This is also the time to set up any sprinklers or irrigation you plan to use.
Water the open subsoil to see if water collects in any puddles, and fill in these places. Replace the topsoil and rake it evenly over the surface.
Spread the necessary amendments and work them in with a shovel or tiller. All types of soil benefit from compost, old leaves or aged manure. Add sharp sand to improve drainage in heavy clay soil.
Leave the ground to settle for two or three months before sowing the grass seed. This will let the microbiotic life in the soil come back into balance. Letting the ground settle also prevents lumps and holes from appearing in your lawn after it is sown.
Pull out any weeds that have come up and dispose of them. Use a soil rake or a shovel to smooth out the ground again before sowing.
Tamp the soil down by walking over the entire surface or using a garden roller. This keeps the seeds from rooting too deeply. Do this step when the ground is dry. Walking or rolling wet soil compacts it, which upsets the balance of microbes and reduces air circulation.
Water the ground thoroughly the day before sowing the seed.