Shut your computer down when not in use to save electricity and reduce wear on your system.
Use a power bar with an integrated timer to shut off all devices and save on "phantom power" or "standby power", the electricity that's used by electronic devices even when turned off.
When replacing your computer, look for an ENERGY STAR qualified model which is 15 to 40% more efficient than older models.
Laptops use less energy than desktop models.

Choose a flat-panel LCD computer monitor rather than a regular cathode ray tube (CRT) monitor. Flat-panel liquid crystal display (LCD) monitors use less electricity than comparably sized CRT models. Remember, the bigger the monitor, the more energy it uses.
Make sure any computer you purchase has an automatic power-down function that will automatically switch the monitor into sleep mode (preferably a deep sleep mode) after a preset period of inactivity. (A feature mandatory to bear the ENERGY STAR symbol).
Ink-jet printers use 90% less energy than laser printers.
A screen-saver doesn't save energy.