There are various causes for grass to die in patches. There may be too much traffic on a certain area, an insect problem or a disease. Repairing your lawn quickly and correctly is important. However, identifying the problem will save you from having to repair the same area over and over again. Some problems, such as severe compaction of the soil or poor drainage, may require you to do a complete renovation.
Prepare the area for replanting by loosening the soil.
Remove any rocks or roots and rake the soil smooth.
Sprinkle grass seed generously over the area you are reseeding and rake lightly to bury seeds approximately 1/4 inch under the soil.
Water lightly every day or two to keep the soil moist while the seeds are germinating. Germination will occur in 4 to 6 weeks. Allow minimal traffic during those weeks.