Lights off from 20:30 to 21:30 today. TVs and computers off too.. and don't drive your car between 20:30 and 21:30. Take the battery out of your laptop, your mobile, and unplug the videorecorder and the refrigerator.
I made that last sentence up. Although if you are a perfectionist, that is what you will do. If you are not a perfectionist and just want to show other people that you are conscious there is a problem and willing to participate in a solution, you can simply turn off the lights.
Hong Kong in the dark, and there hasn't even been an earthquake!