One of the big things we all can do in every day is substitute a bad choice with a good choice. Instead of using a car to go down the block, take a walk. Instead of using incandescent light bulbs buy Energy Star certified florescents.
One of my favorite ways to change my habits was to change which fish I ate. The fishing industry can severely damage the ocean through over fishing, bycatch and ripping up the ocean floor. The obvious looking solution may seem to be to stop eating fish. However, this may be wrong. There are fisherman out there that really care about the ocean and have tried to switch to better fishing methods and more sustainable fish stocks. By supporting these fisherman we can be positive consumers and make an impact on the industry.
One easy way to be sure of the fish you are eating is to know the resteraunt you are eating at. Legal Seafoods. They are wonderful. They were the first resteraunt to bad Chilean Sea Bass, which is a freshwater fish that is nearly extinct due to fishing pressures.
The somewhat harder way to make a positive impact with fish choices is to learn about the individual fish. I recommend this website.
http://www.mbayaq.org/cr/cr_seafoodwatch/sfw_regional.aspxChoose your region. I usually have cards with all the regions with me at all times. I call it my "fish bible". I almost never eat fish because I am vegetarian and fish is meat. Once in a while I cheat in order to support fisherman and help others to see that good choices taste good. My family regularly asks my which fish are good and which ones aren't. Even my friends ask me.
If you have a favorite whitefish and it's on the bad list, look for a whitefish on the good list to substitute. This is one really good way to help the environment while supporting the few industries that are on our side.