Check the thermostat on your water heater to ensure that it's not hotter than it needs to be --120 degrees is plenty hot.
Wrap your hot water tank with an insulating blanket and wrap the hot water pipes with insulting tape or foam. These materials are available at hardware and home improvement stores, and takes just a few minutes to do (see video).
Install modern "low flow" heads on your shower and aerators on your sink faucets. These efficient fixtures are easy to install (see video). All you have to do is just screw them on, and they will use less than 1.5 gallons per minute instead of 2.5 gallons or more for older models.
New water heaters are much more efficient than older generations. An average water heater will last about 10 years, so when it's time for a replacement, look for the Energy Star label to ensure you are getting the most efficient one. New types of "tankless water heaters" that produce hot water only when you need it may also be worth a look. These are commonly used in Europe and are a sensible alternative to keeping a full tank of hot water on hand at all times, even when you're asleep or away.