Turn off computer, lights, stereo and every other appliance in your home when not in use. And do this from the main supply, leave nothing on standby. Only have electricity running in the room you are currently using. Everywhere else is wasteful (and harmful to the environment)
Eliminate Vampire Power - Unplug adaptors and chargers when not in use
Use compact fluorescent light bulbs (CFLs) instead of incandescent light bulbs. The initial cost is more, but they save huge amounts on your electricity bill and last 12 years.
Use cooler wash cycles for your clothes and as far as possible avoid using a dryer which gobbles energy. Use a clothes rack instead.
Do your own dish-washing rather than using a dishwasher. Use left over water for garden.
Don't leave the water running while brushing your teeth.
Don't flush the loo every time you go, i.e. after wee jobs.
Take showers instead of baths.
Turn your refrigerator temperature down (while retaining a healthy level). Most refrigerators are set at a temperature that is unnecessarily cold.
Turn down your heating. Don't know where you live, but it is unreasonable to heat houses to summer temperatures in winter. In winter wear winter clothes, even indoors.
Consider energy-efficient computer systems and monitors when you replace a system. Flat-screen monitors use 50-70% less energy.
Check your faucets for drips which can waste several gallons a day.