If your lawn sits on a slope, it will need special treatment to protect seedlings from rain runoff. Materials like straw is good to cover the seedlings to protect them, but must be removed as soon as the grass begins to grow. New seeding can be covered with open mesh burlap or cheesecloth or a special garden supply stock of open mesh cloth as well, and these can be left out as they rot and become part of the soil.
These methods will not only protect the seeds from washing away or erosion, but also keeps the soil moist, prevent any sun exposure that can damage seeds. Plain burlap or cloths should be removed when the grass sprouts are 1/4 to 1/2 inch long.
Seedlings will do best with a natural rainfall, but if the weather is dry, you must water the seedlings for germination to occur. It is best to water in the morning, with a fine mist like spray so puddeling of water or crusting will not occur.
After the seed begins to sprout, the moisture supply must be constant or the plants can die. For level places use a sprinkler and get the soil wet at least 5 inches with each watering, be sure not to over water though so the soil does not become waterlogged and too compact. For slopes use a canvas hose, or wrap the hose in porous canvas, so that the water will pour slowly in big drops inking into the soil quickly, instead of running off.
Seed mixtures tend to developed unevenly when they are new plantings. The "nurse" grasses (such as rye grass), and the semi-permanent types grow fast and can damage the slower-starting permanent grasses as they compete for moisture and soil nutrients. Therefore begin mowing when the tallest grass is 2 inches, but you should never mow anything under 1½ inches.
Renovating Old Lawns
If you have a poor lawn that does not seem to grow grass, you might just as well do something drastic with it, possible rebuilding it completely. Just be sure not to repeat the same mistakes. Take notice to any puddles or pools that remain on your lawn for long periods after rain. This means you may need to lay drain tile or get a good layer of gravel under the topsoil. If your landscape issue is hard-baked soil and the grass is thin and anemic, the best method is spading up or plowing followed by soil preparation and reseeding.
If limited areas get too packed consider loosening or cultivating the soil, or aerate the garden by opening it to a depth of 6 or 8 inches. This can be done with an ordinary spading fork, driven deep and worked back and forth to enlarge the openings. Brush sharp sand or compost into the holes to allow for better movement of air and moisture through the soil. Many poor lawns are due to poor soil, which may need fertilizing and feeding.
You need to use 4 pounds of plant food for each 100 square feet of lawn. If you have thin grass, add new seed and use plant food. You can level out a bumpy lawn by raking top-dressing into the hollows, or peel back the sod, filling in the hollow with good soil and replacing the sod. A mossy lawn is a result of poor drainage, not acidity in the soil, meaning the drainage may need a change for improved drainage, or raking and liberal fertilization.