Over Seeding
Grass is no different than any other plant, in that it becomes less efficient as it ages. To combat this reduced efficiency, one of the best things you can do for a lawn of any age is to inject some new life into it by over seeding.
Our preference is to use our slit seeding machine (which drills the seed into the soil), because it over seeds and aerates at the same time, which is a nice bonus. However, the slit seeding machine is pulled behind a tractor, so there are areas (eg. Backyards) that are inaccessible, and therefore must be overseededed using a broadcast spreading method. This is an acceptable method, but its efficacy does not match the slit seeder.