Moss is a slow-growing plant that thrives in areas where other plants cannot grow. Moss typically appears in yards in late winter and early spring if the ground as been saturated all winter and some of the grass has died off. Thankfully, moss is easy to control and eliminate with some consistency and an improved green thumb.
Aerate the lawn. Soil requires both minerals and oxygen to sustain rooting plants such as grass. If there seems to be more moss than grass, then the grass has most likely died because of a lack of soil oxygen. Rent a lawn aerator and run it over the entire yard to refresh the soil's oxygen flow.
Test the soil. Soil requires nitrogen and a neutral pH to support healthy grass. If the soil's nitrogen levels are low, add some fertilizer monthly to replenish the soil's supply. If the soil is too acidic (pH less than 7) then add some lime to the soil and till it in to a depth of 6 inches.
Observe the amount of shade that the yard receives. Most grasses thrive in full sunlight and require a minimum of eight hours for healthy growth. If trees or other yard fixtures are creating more shade, then trim them back with pruning shears so that the yard will receive more sunlight. If it is impossible for the yard to receive any more sunlight, then consider planting a shade grass such as fescue grass.