EARTH! FIRE! WIND! WATER! HEART!
GOOOO PLANET!
What do I do for the environment? Well, for starters, I don't drive a car, nor do I plan to ever drive one. I've found that I can go everywhere on my decrepit old bike or using public transport. Granted, me not driving a car isn't solely for environmental reasons, but my resolution not to start driving later on pretty much is.
I also try to do all my sea crossings by boat rather than by aeroplane.
I usually turn off anything that uses electricity when nobody's using it, though I occasionally leave the computer on for a short while because I don't feel like waiting an eternity for the bloody thing to boot up. My habit of switching off lamps occasionally causes annoyance in others.
That's basically it. I also don't litter, and seperate different kinds of trash, but that's kinda normal, really. Well, and I try not to waste too much paper, despite every effort by my school

.
Oh, and like various others in this thread, it always annoys me when someone leaves the water running, but that may also be because of the annoying sound it makes.

Even you can do something to help the environment!
^ Yeah, I know it was cheesy, but it was a wonderful excuse to use the

smilie.