Purchase or rent a lawn roller from the hardware store or a rental location.
Fill the lawn roller with water or sand as directed by the manufacturer and begin rolling over the soil.
Push or pull the roller in a single direction over the entire area to flatten the soil and smooth out bumps. This will ensure grass grows evenly and flat across the entire lawn without divots or lumps.
Water the soil lightly with a misting setting on the hose attachment. Watering loosens up dry, crusty soil and also prepares the soil for spreading lawn seed. Overwatering the soil can create mud, which will make it impossible to rake after the seeds are spread.
Spread lawn seed over the soil and lightly rake to combine the two. Raking will also spread the seeds around so you don't have large clumps of grass growing in a certain area. In areas that don't have many seeds after raking, add more seed to that location.
Moisten the soil once again with a misting attachment to help the seeds begin the germination process.