Lawns require care and maintenance to stay flush and full. There are a lot of factors that can affect lawn density. Lawn moss can cause grass to suffocate and die. Grass thatch (dead grass left from mowing) can cause a lawn to dry up, lose oxygen and die in patches. Aerating the lawn, dethatching and fertilizing properly will help your lawn breathe, ensure it can receive nutrients and help new grass to grow.
Improving your lawn.
Mow your lawn so that it is short, about 1 inch high, so that thatch is easier to see and remove.
Run a dethatching rake throughout areas of the lawn where dirt is hard to see between the blades. Run the rake at a slight angle to break up the thatch and remove it by hand if necessary.
Water the soil two days before aeration so that it is moist (not wet).
Aerate your lawn using a power-core aeration tool, or with a hand-held aerator by pushing it down into the soil, and removing plugs from the dirt. This helps the soil breath and expand by freeing compacted dirt. Run the aerator in two directions across the lawn for best results.
Apply a slow release fertilizer to your lawn in the spring to promote grass growth. Apply 1 pound of nitrogen per 1,000 square feet of lawn. Another application of fertilizer should be done in June or July.