STOP BUYING STUFF THAT YOU DON'T NEED, USE, OR LOVE
Really, it's that simple. Here's why.
Let's consider the basic economic principle of supply and demand. As demand for a good decreases, the supplier will decrease the production of the good. With me?
Now let's consider how the Earth comes into play in this scenario.
NATURAL RESOURCE > PRODUCTION > DISTRIBUTION > CONSUMPTION > LANDFILL
If you want a more detailed description on what goes on during each process, check out The Story of Stuff.
Bottom line: Less useless stuff that is produced=less useless stuff that will be thrown into a dump. It's better for your peace of mind, your wallet, and the Earth.
If you want ideas on how to stop mindlessly consuming, check out The Minimalists.
(Also, they are screening their documentary Minimalism in May 2016, so find a theater near you to check it out.)