Be prepared to save the environment by starting off simple. Be aware of your surrounds, speak up, don't be afraid of your rights.
Donate! Donating helps organizations such as GreenPeace fund there projects to help make earth a better place. They will work to prevent catastrophic environmental problems.
Volunteering is the easiest way to become a environmental activists. There are so many things to do when you volunteer from licking envelopes to climbing smokestacks. Also you dont have to start big, like a big organization you can start locally!
An important step into becoming an environmental activist is helping recruit others to help our Earth. For example, you can talk about your campaigns and victories in, and make sure your friends know how you're making a difference in the environment.
If you dont know something don't be sad. An example would be that you have to have the answer to climate change. When you talk to people about taking action to slow climate change, you will be confronted by a someone who is eager to argue that what you are doing is not the answer to climate change.