With the advent of online bill paying and shopping, you are able to conserve trees as well as automate your financials. If the companies you do business with offer the option of "e-Statements", "e-Bills", or "Paperless Statements" take advantage of this. Not only do you save paper, but you also reduce the chances of your bill or statement being lost in the mail. Along this line, consider paying the bills online (thus saving checks, envelopes, stamps, and worries about your check being lost). And shopping online will save gas and time.
When you have to print something out, reuse paper when able. If you have something that you printed out on one side, use the other side for a different print out. Most printers and software will allow you to print on both sides of the page. This is a much "greener" option than printing one page on one piece of paper.