Turn off the lights? 'How obvious', you say! Yet, the reality is that while we know this is the easiest thing to do, many of us still just can't get into the habit.
Make this a game. While you are learning to turn off the lights when you leave the room, begin a game that has you run about the house, every hour on the hour, turning off the ones you missed. I'll bet you'll be surprised at how many you've left on. After a few days of this, I can pretty much guarantee that you will have made turning off the lights a bit of a habit. Teaching kids to turn them off each hour can be fun - it's a race to see who can finish their area of the house first! If they are wiley - they'll figure out they can win by remembering to turn them all off in the first place.
Turning off the lights can make a noticeable difference in your hydro bill - so this is not only an energy saver - it's a guaranteed money saver, too!