This is what I do:
1. Always turn off completely all the computers - no sleep, no hibernation, PSU switch to off when not using them. Also turn off the monitors.
2. Do NOT overclock, use down-volting - reduces energy both for operating and cooling.
3. Check the outside temperatures, when it is colder then the set temp inside, open the windows, don't use air conditioning.
4. Tablets, phones can be charged in the car while commuting - you are using gas anyway...
5. Use LED lights where you can.
If it is a business - use motion sensing light switches... there is no reason to have the lights on when nobody is in the office, kitchen, restrooms...