Very simple and basic ideas that are easy to do, but hard to make a habit for most.
1. Unplug unused electronics
2. Power down computers
3. Turn off lights when not in use
I know the current policy is to keep computers on for patches and updates, but I'm not sure this is entirely necessary. I know more recent versions of Windows does not take long to update, and surely anything our IT is doing can adjust to a sign-in update. A few extra minutes waiting to update will save a ton over a year.
Plus, computers do have lifespans, and having them on all the time certainly doesn't extend them.