The number one thing you should do is educate yourself about the issues. It's hard to do anything constructive if you don't understand the facts. So spend some time researching issues such as Global Warming, Recycling, Energy Consumption, etc... Don't take the politicians word for things, read lots of different articles and make your own conclusions. After that, share your knowledge with a friend, a co-worker, or a family member.
Increase your Recycling. It is one of the best ways to help the environment. Recycling reduces garbage in landfills, reduces carbon emissions by reducing manufacturing and transportation emissions and enables our Earth's natural resources to be more evenly distributed among the world's population. Consider drinking water from the tap. This may seem like a strange concept, but tap water in NYC is among the tastiest and purest in the world. It contains fluoride, which will keep your kids teeth healthy. You can always refill your water bottles from the tap so you have water on the go, and the savings will soon add up enough so you can buy some jewelry :)
If you've never wrote your congressman or woman, now is the time. We need our government to legislate changes that reward green behavior as well as to fund the development of renewable energy. It might not be this crazy carbon tax, simple things work better and can be done sooner. Vote for politicians who share the same Green values as you, and tell them to give up their chauffers and ride the subway like I do.
If you're in New York, attend an earth day event. The streets around Grand Central Terminal will be closed for an Earth Day fair, come and see what's going on. Almost every community has things planned for this day, look in your local paper. If you have a yard, plant a tree!
We take time in the studio every day to recycle, we've switched to compact fluorescent lights to save energy (and it works!) and we've programmed our computers to go to sleep after a few minutes, and we have reduced paper significantly by storing documents electronically. Our catalog, that was a huge brick of paper that ended up in landfills every three months, is now online. There's more to do, but you have to start somewhere. Earth Day is the time to educate yourself and commit to doing something to help preserve our environment. Ciao!