This one is pretty obvious, but still you see some people who just dump out old oil, antifreeze, etc without thinking about it's impact on the earth.

Nearly every household has some kind of hazardous waste: old paint cans, used motor oil, unused pesticides and weed killers.  If you dump these things down the drain, you'll end up polluting the water supply.  Old Batteries, CFL Light bulbs, and other hazardous solids should be considered as well. They should be disposed of in a site specially designed for hazardous or toxic wastes.  Some cities and counties have monthly or annual pickups.  Other areas have special drop-off sites.  Call your city or county government to find out the proper way to dispose of such trash in your area.  Try organizing a hazardous-waste-collection day in your neighborhood or at your school, encouraging others to dispose of materials properly.

As always, feel free to comment with questions, or if you have anything to add