Notices by every lightswitch encouraging people to turn lights off whenever they leave a room.
Lights in communal areas (toilets, corridors, etc.) timed to switch off automatically outside office hours. Perhaps install a movement sensor to switch the lights back on again for a few minutes.
Radiators to be turned off in toilets.
Powersave mode activated on all monitors so they are switched off automatically after a period of inactivity.
Encouragement to turn off all monitors and computers overnight unless absolutely necessary. (leaving one computer on every night for a year produces an excess of about 400 kg of CO2; so an office of 100 people could save about 40 tonnes of CO2 per year just by turning off their PCs every night (0.2 kW x 14 hours x 365 days x 0.43 kg CO_2 per kWh = 440 kg of CO2 per year)
Greater recycling provision, e.g. paper recycling box in every office, plastic/glass recycling in kitchen/common room. It's important to be able to recycle news papers and cardboard as well as just office paper.
Signs in the communal kitchens saying: "Only fill the kettle with as much water as you need. Never boil more water than you need. If the kettle is on for only 2 minutes per boil then you emit about 100 kg of CO2 every year. If it's on for 4 minutes per boil then you emit 200kg of CO2. (2 kW x 365 days per year x (2 min/60 h/min) x 10 times per day x 0.43 kg of CO2 per kilowatt hour = 105 kg of CO2 per year)"
Encourage people to buy LCD screens rather than CRT (17" LCD uses ~40 watts; 17" CRT uses ~250 watts; CRT uses 6 times more power)
Bring own kitchenware. Avoid using paper/foam cups or plastic forks and spoons.
Set-up box for collecting electronic waste. Those will increase the rate of recycling batteries, electric bulbs, and also reusing some of old electronics.
