Water early in the day if possible.
Given a choice, water early in the day when lawns are normally wet from dew. Avoid midday watering due to excessive evaporation, and at night due to potential increased chances of some diseases gaining a foothold. The exception to this guide is when you are in extremely hot weather and nighttime temperatures don't go below 68 degrees. Then it is better to water in the late afternoon or early evening, providing you don't have watering-time restrictions. Early or late in the day reduces the amount of evaporation that takes place during the very hot day, allowing more water to reach the root zone.
Spread the water uniformly across the lawn.
Sprinklers vary in distribution patterns, and require spray overlap for uniform coverage. Placing coffee cans or similar straight-sided containers on the lawn can help measure water application rates. Avoid flooding areas, or missing other spots. On heavy clay soils and slopes, watch for excessive runoff; it may be necessary to apply the water in several applications to allow for adequate penetration.