Consider the size and shape of the shadow a plant will cast. At midday a vine-covered wall is cooler than a bare wall. If you don't have mature trees, consider planting vines on a trellis. Water Water also tempers heat. Even a small pond can help.
Plants can also alter microclimates by intercepting precipitation.
Because trees intercept and slow down water movement they also help to control runoff and erosion. Plant water-thrifty plants, often natives that are suited to the climate. Group together plants with similar water needs. During droughts raise the cutting level of your lawnmower to between 2 and 3 inches. This causes less stress and encourages deep root growth.