Step 1: Reuse
Look at all the stuff you are throwing away. Cans, milk jugs, bottles. Think of all the things you could make with those things!
Here are a few ideas to get you started:
the body for your next electronic project.
mould making material (I know an instructable that uses milk jugs to vacuum form.)
Step 2: Recycle
Recycle. Why throw away all of those beer and pop bottles, when you could take them to a bottle depot and make money?
Have things you aren't using? Sell them on sites like ebay!
Step 3: Compost
Love to garden? You can save a ton on soil if you compost.
Step 4: Shop Smart
Better than shopping: Trading. There are websites where you can trade something you don't use or want for something you do. It can save a lot of money.
Looking for a site? You can, sell, trade, barter and give things away on craigslist.
Step 5: Going the Extra Mile.
Going the extra extra mile. Clean up your street or the area around you. Now thats going the extra mile!
You could probably think of a ton of different ways to help the earth, but their just ideas until you put them into action.