No, not the lights! (although that is a good place to start!)
What I mean is turn off your cell phones when you don't need it on. I find that when I leave it on (which I'll admit to doing often!) that battery just runs low quickly and I have to charge it all over again.
So from now on I'm going to remember to turn it off as much as possible. Besides, when I'm home I have a land line anyway. If someone truly needed to reach me then I have that line.