Here are a few that I do:

-take a backpack or duffle bag to carry groceries
-drive your bike (or skateboard, or whatever) for anything under 10 miles
-keep windows open and use natural light instead of electricity
-but only fresh fruits and veggies
-buy meat, dairy, and eggs w/o growth hormone
-buy in bulk to avoid extra packaging
-make sure your computer has the energy saver sticker
-DON'T BUY STUFF YOU DON'T NEED
-invest a set percentage of earnings so that I can buy a house/car/retire/whatever later rather than spend it on useless stuff now (also, you can invest in mutual funds that only support green and socially conscious corporations)
-turn off the TV and read a book, thus avoiding dumb programming AND alluring TV ads
-make lists when you go shopping to help avoid impulse buying
-carpool or use public transportation
-support small businesses (ie buying veggies from the Saturday market or family owned store instead of Safeway/ going to the local indy CD store instead of HMV or Best Buy)
-give away my old Nike's and clothes instead of trashing them
-print out drafts and other stuff on the clean side of previously printed out stuff

----------------------------------------
All great truths begin as blasphemies.
--George Bernard Shaw