If you plan to drink your coffee at Starbucks, tell the barista that it's "for here." They'll put it in a mug for you rather than a paper cup.
Check with your local grocery store to see if they recycle plastic bags. Most do these days, and even if you use re-usable shopping bags for your grocery shopping, you can bring in other types of plastic bags like ziplock bags or other bags used for food packaging to be recycled instead of just adding more plastic to the landfills.
Check out the products at Preserve Products and pick up some toothbrushes made from recycled plastic. And then, when you're done using them, you can send them back to Preserve Products, in the packaging they provided when they shipped them to you, and they will recycle your toothbrushes, to give them yet another life!
If you have stuff that you need to get rid of but don't have time to donate or have a yard sale, don't just chuck it. Check out Freecycle.org which will direct you to local freecycling groups. It's a great way to reduce land fill and put your stuff to good use for someone else. It's also a good way to find free stuff.
It's time to replace those incandescent bulbs with CFLs, or compact fluorescent lights. CFLs use 75% less energy than incandescent bulbs, and can last up to 10 times longer. They don't buzz or flicker, and most turn on immediately. The color and quality of the light may take a few days to get used to, but the savings are worth it.
Carry your own coffee mug when you go to Starbuck or Peets. They even reduce 10 cents off your bill for your green gesture
Go easy on the paper kitchen towels. Look for brands that have half sheet option. They do the same job as well that a full sheet does.
Wait until you can fill up your washing machine before running a load of wash. Then you are maximizing the use of water for washing. Also, dryers are more efficient when they are more full. Don't just throw a pair of socks in by themselves to dry.
Turn off your car when you aren't moving. According to one source, "An idling engine produces 50 to 100 more emissions than a warm engine. Plus, cars get the worst gas mileage when idling cold or warm. Gas is being burned for no forward motion."
When accelerating while driving, do so slowly. Putting the pedal to the floor uses more gas and is more inefficient. Try and keep the RPMs under 3000 for the most efficient driving.