Turn your computer off. Computers are some of the biggest energy users in offices. Turn your monitor off when you leave your office instead of relying on a screensaver.
Turn off lights and electronic devices when not needed and when you leave for the day or weekend.
Use your shades for comfort. Save energy and keep your office comfortable by lowering shades to shade your office during hot, sunny days and to keep your area warmer during winter.
Take the initiative by turning off lights, fans, or room air conditioners in unoccupied space on your floor. Note that there is no cooling benefit from fans being used in empty rooms.
Go green during longer breaks. Turn off some of the larger items in your office such as the photocopier, printer, coffee machine, etc. if your colleagues are amenable.
Use a reusable mug or bottle for water, coffee or tea.