amend lawn soil
Soil improvement after a lawn is established is difficult because to comply with Maryland's Fertilizer Law, the amount of compost that can be applied (topdressing) has to be dictated by a soil test and a compost analysis. You can also work with a lawn care professional who is a certified professional fertilizer applicator if topdressing is desired. Usually, this is not necessary for an established lawn where soil organic matter has increased over the years through the addition of grass clippings, leaves, and dead plants and microbes, as compared to the soil in a newer development that was stripped of topsoil during construction.
There are no easy answers other than starting over for a new lawn or renovation projects where compost is incorporated into the top 6 inches of soil. See more on our Organic Lawn Care page http://extension.umd.edu/hgic/topics/organic-lawn-care
At this point you can leave the grass clippings on the lawn, mulch leaves with your lawn mower, and aerate in the fall. The decomposed roots over time will make their own top soil.