I know it might sound overly simplistic, and it's far from the only lifestyle change I have made or plan to make to lessen my environmental footprint, but my most recent change for the good of the environment is to make sure that I have at least one day each week when I do absolutely no driving.
That means no driving on my own and no driving caused by me, such as having a pizza delivered. I can't control things like mail delivery, unless I make my no-driving day Sunday every week, which I haven't been able to accomplish.
I hope to eventually increase my number of no-driving days each week.
So, what have you done to lessen your footprint on this Earth?