It doesn't get much simpler than this: Check your settings. Activating your computer's power-saving features can cut your computer's energy consumption by 50 percent or more.
Most computers come with power-saving modes (if yours doesn't, it's probably time for a new computer). But lots of those computers ship without the settings activated, so you have to take a minute to turn them on in order for them to work.
In a computer without power-saving features, there are only two power modes, on and off. In on mode, the computer is using its full number of watts. Energy-efficient settings set up additional modes, so instead of just on and off, you've got on, sleep, hibernate and off, plus a mode that just dims or shuts off the display (which typically consumes the most power). Each successive mode uses less energy, and you only have to hit a key to reactivate the computer out of sleep or hibernate mode, instead of having to boot up all over again.
All you need to decide is how long you want the computer to wait before activating a lower-power mode when there's been no activity. If you often spend long chunks of time staring at your computer screen and not touching anything, you may want to set sleep mode to activate after a good while, like 20 minutes. If long periods of inactivity are rare for you, you could save even more watts by setting sleep for something like four minutes.
Each computer works slightly differently, but you can usually access your power settings through the control panel. It takes about 30 seconds to make some high-efficiency changes.
Up next is perhaps the most underused, supremely logical power-saving method out there.