A dishwasher uses almost as much electricity annually as a dryer or a freezer. Most of the energy is used for heating the water, so the best way to improve efficiency is to cut down on water consumption.

The most water efficient dishwashers on the market today are using about 5 gallons of water per load; less than half the amount of the least efficient ones. Half the water means half as much energy to heat that water.
You can save energy by choosing the energy saving and air drying cycles. Heated drying draws a lot of electricity while the circulating fans for air drying use little. Scrape your dishes before washing instead of rinsing and wait until you have a full load before running the dishwasher.

hand washing
You can save hot water by hand washing your dishes; IF you do it efficiently. This means washing a whole load at a time, and rinsing in a tub of water instead of letting the water run. A faucet aerator will save as much as half the water used by a standard faucet.