Keep your lawn and garden weed-free. Weeds compete with your plants for water, oxygen and minerals! Cultivate soil regularly to keep it loose. You'll use less water because it will penetrate more rapidly and deeply.
Put a layer of mulch around trees and plants. Mulch will slow evaporation of moisture and discourage weed growth too! Avoid watering on windy days. Wind can blow water away from cultivated areas and onto concrete and asphalt where it's not needed. Don't let your sprinkler water the sidewalk, driveway or street. Put the water only where it's needed!
Talk to neighbors. If you live in an area where watering is commonplace, set up a schedule so everyone's not watering at the same time!