Purchase quality grass seed. Resist the urge to buy the cheapest seeds, as this may be inferior. Look for disease resistance and drought tolerance. High quality seed also produces the richest and greenest grass.
Loosen the top ¼ inch of soil on any bare patches you find on your lawn. Be sure any existing grass has been cut short. Smooth areas level, and remove any rocks or other debris.
Spread seed by hand for small areas. You will need approximately 16 grass seeds per inch of lawn.
Cover the seeds with ¼ inch of soil. You can do this with your hands or with a lawn rake. Add starter fertilizer found in the hardware store. Follow the directions for application.
Water to moisten the seeds. Spray daily to keep the seeds evenly moist. Once grass appears, water to keep the roots from drying out. Once established, decrease watering gradually. Adopted from http://www.ehow.com/