When it comes to using the toilets themselves, be sure you're reaching for toilet paper created from recycled sources—remember, "rolling over" is better than "rolling under"—and avoid using products made from virgin boreal forest trees. The Natural Resources Defense Council has a solid list of recycled paper sources, so you aren't literally flushing virgin trees down the toilet.
Get the NRDC's list of recycled paper sources
And when it comes time to flush, close the lid before hitting the button to prevent the spread of bacteria around your bathroom. Ready for the next step? Install a dual-flush toilet or dual-flush retrofit on your current toilet.