Yardsmarts of www.yardsmarts.com give a compact little video (1 min 43 secs) that should leave you in no doubt as to how to fill in that bare patch in your lawn or establish a lawn in a bare yard. The principles are the same no matter the size area you want to seed.
The Yardsmarts commentator recommends spring or fall for planting in the Northern US states which are cooler and summer for the Southern states. You go out and buy a sack (or sacks) of good quality grass seed. Before leaving the store, read the label. Weed seed (there is always some mixed into the grass seed) should amount to no more than 0.2%.
Right, so you go home and prepare the soil by raking it. Then you spread the seed either by hand or using a small spreader (for small areas) or a broadcast spreader (for large areas). The idea is to get about 15 seeds per square inch. Then you tamp or rake the seeds into the soil (small area) or heavy roller (larger area).
Then you need to spread straw or peat moss over the area to keep the seeds in place while they germinate and keep the soil moist. Finally you water the area gently and keep it watered whil the lawn is getting established. Water it twice a day if necessary. You don’t want it to dry out.
