Educating yourself and others about the world's state of being and being conscious. Making earth-conscious decisions are not difficult once your know what you're doing (hence educating yourself). The first steps are quite easy - remembering to turn the lights off when you're not in the room or not using them, catching run-off water for other uses such as the toilet or watering plants, using cleaning products that are chemical free, good for the environment and easily made at home. Another way is winter-proofing the house. An easy way of doing that is going through and checking for cracks in doors and window frames (which I used to have lots of) and stuffing them with news paper. It's amazing how well that keeps the drafts out.
Recycling is a huge thing, and buying local, looking for the carbon food print of where your food comes from, how far it travels just to be packaged, what the packaging is made out of, can it be recycled, and so on.
Looking into what you can do for yourself is a great way to keep the world green. Do I really need to buy this laundry detergent, or can I make it out of baking soda and vinegar? Do I really need to buy these carrots, or can I grow my own?
Growing your own produce enriches the earth, especially if you are making your own soil/compost. It is healthy for the earth, and deepens your relationship with the earth.
Instead of Buying new clothes, look into what you can do with your old clothes. Patches can be made out of completely unrestorable clothing, while other clothes can be altered into a whole new style.
I feel like with the explosion of new technologies which make life easier for us, we have lost a little bit which makes us human. We have lost our creativity because we don't need to be as creative with how to survive and keep our environment fertile. It's easier to sink into "going through the motions" simply to survive, and turn off the brain, and not think about the world.
Education, passion, and love are what are going to keep the world clean and green. A meme I've seen floating around which I love so much says "I wish people put as much energy into loving the earth as they do toward the one who created it", or something along those lines. It's very true, and I think people need to remember that this isn't just our earth. It's everyone's, and that includes EVERY living creature, not just us human folk.
