Brown spots in your lawn may be caused by a lack of nutrients. Perhaps you had something like a trampoline sitting on the grass, blocking sunlight and rainfall. Either way, fixing the brown spots will make your grass look lush once again.
Loosen up the soil in the planting area. Run a metal rake or rototiller over it, depending on the size of the brown spot. Dig down so the top 3 inches come apart.
Break up soil clumps, remove debris and dig up weeds. Soil clumps that are smaller than 1 inch in diameter will not affect the germination process.
Spread a fertilizer that's high in phosphorus to the brown area. You can also use a starter fertilizer, which is specifically formulated for grass seed. Spread it by hand or through a hand spreader, following the instructions on the label to determine how much you need per square foot. Break up large clumps of fertilizer before dropping it on the soil.
Mix the fertilizer into the ground surface with garden tools. Smooth out the area with a metal rake. If there are any low-lying areas, fill them in with soil. Dips will result in pooling water, which will make the grass seed wash away.
Sprinkle grass seed in the brown spot by hand or with a hand spreader. Spread enough so there are no bare spots, but don't drop too many seeds because they will compete for nutrients. Gently rake over the seeds to cover them with a thin layer of soil.
Set the hose on a fine mist and water the grass seeds until the ground is moist. Use the finger test daily to make sure the lawn surface stays moist until the seeds sprout. The exact amount of water depends on the climate and other factors.