Increasing the soils ability to hold water reduce the need for irrigation systems and hand watering. Adding organic matter such as compost or peat moss is very effective. Add compost and other other organic matter to the garden also great for plants as the root system will be able to grow deeper into soil resulting in healthier plants. Roots tend to stop growing vigorously when they reach dry soil. Having good soil conditioners added to the garden will also prevent quick water evaporation on the surface. The use of mulch in the garden also will help to conserve soil moisture.
If your garden is without a few shade trees, plant one if you have the space. The shade it produces will help prevent water loss. Plants which are properly planted and planted in the right location also will need less frequent watering. A shade loving perennial like astilbe, for example, if planted where it gets to much sun will demand lots of water as it wilts in the hot summer sun.
Native plants generally adapt the best to the climate and are therefore easier to grow and care for. Also, select plants described as drought resistant.
Water retaining gels, sold at most garden centers, are great for smaller gardens and containers which tend to dry out quickly and need frequent watering.
Diverting water from roofs and other hard surfaces with pipes and collecting it and storing in barrels is a great way to conserve water. Be sure to use water front non-contaminated areas. Driveway are probably not the ideal area to collect from.