Grass seed needs direct contact with soil to germinate. You'll get better results if the soil is loose and aerated. Till the planting area 4 to 6 inches deep for best results, and remove debris before spreading grass seed.
Hand and mechanical spreaders are available for seed dispersal. Hand spreaders are best for small areas and for overseeding, whereas mechanical spreaders are more effective in larger yards.
Cool season grasses grow best in the northern part of the country. Disperse those seeds at the beginning of fall or spring, to avoid times of frost and summer heat. Warm season grass grows well in southern states. Sow those seeds at the beginning of summer.