There are two hard and fast rules when caring for a newly seeded lawn: It is difficult to water too much and stay off the grass bed at all costs--and keep your dog off. Grass seeds need very moist soil to germinate. Once they do germinate their hair-fine roots cling tenuously to the soil. Any disturbance will sever the roots and set back the lawn's establishment. Adequate nutrition is also helpful, as many nutrients are washed through the soil with frequent waterings.
Keep all foot traffic off the seeded lawn. Cordon off the space with visual markers and tape or rope to alert all passersby to remain off the soil surface and dissuade animal visitors. What may appear to others as a patch of dirt is your future green glory. So provide a heads-up with a well marked zone.
Water gently once or twice daily for at least three weeks or until the green shoots are an inch or so high. Use an adjustable-nozzle spray head attached to your hose. Then cut back to watering every other day for two weeks and taper off some more until you are down to once a week deep watering. Use the mist or light rain setting on the spray head to prevent the soil and seed from being displaced and to avoid creating divots in the soil. This can happen if the stream of water is too strong. Keep the soil moist at all times and make sure the edges of the seeded area are wet; they tend to dry out most rapidly.
Feed your newly seeded lawn with a second dose of granular lawn starter fertilizer two weeks after the seed was sown. If you applied a starter fertilizer when seeding your lawn, you can use the fertilizer again, following the label directions. If you did not use a starter fertilizer at planting, apply any lawn fertilizer recommended for your type of grass. Water well after applying. Feed again one to three times a year as needed throughout the life of the lawn.
Refrain from walking on or mowing the new lawn for as long as possible or until the grass is at least 2 to 21/2 inches high. At this height the roots are somewhat established and you can mow safely with a sharp, clean blade. Remove no more than a third of a grass blade in any one mowing session to prevent shock to the lawn. Lower the blade height in subsequent mowings if desired.