Quality grass simply needs water, air, sunlight and nutrients. In most areas, grass needs approximately one-inch of water a week. Infrequent and deep watering encourages deep roots and a healthy lawn.
Mow frequently enough (with a sharp blade) so you never cut-off more than one-third of the grass blades in a single mowing. This will also allow you to leave the clippings on the lawn so they can naturally decompose and return nutrients to the lawn.
Prune trees so they allow as much light as possible onto the lawn.
Fertilize at least biannually, or according to the specific needs of your lawn.
Aerate every other year to reduce compaction and increase the exchange of water and air at the root level.