The first eco-friendly step that I ever took was when I turned vegetarian at the age of 17. The change was quite illogical and poorly-planned. I had many friends that were vegetarians, some of whom had never before eaten meat, but that had never phased me. My roommate in boarding school was a vegetarian and I distinctly remember her showing me a fairly disturbing PETA pamplet. Still, unphased.
One afternoon, however, I was in the school's library, poking around, and came across a Buddhist textbook. Although most of the content has long-since been forgotten, there were repeated passages about respecting life, which for whatever reason impacted me greatly. Since that afternoon I have been a vegetarian, although the strictness of my diet has changed as my attitudes and opinions have evolved. At one point I thought about returning to eating meat but then read "Diet for a New America" by John Robbins and that was that. I am currently a lacto-ovo vegetarian, but I also eat fish, so in many ways I do not consider myself to be a "true" vegetarian. I'm at a point in my life now where the labeling is not very useful as it is always followed by such a long explanation, or worse yet, an argument about ethics, which I'm not inclined to get involved in. For the record, I personally do not take issue with anyone else's food choices, nor do I want others to try to convince me of the merits of theirs.
For those of you that are vegetarian, there is ample evidence to suggest that such a lifestyle is both environmentally and economically beneficial. Two helpful statistics that I have come across lately are that being a vegetarian (or nearly-vegetarian) can literally reduce your carbon footprint by a tonne a year (meat-eaters average 2.5 tonnes or so) and by just cutting one average-sized meat-based meal per week out of your diet, you can save $100 over the course of a year. For those of you that are meat eaters, regardless of whether or not you intend to ever stop eating meat completely, those are two excellent reasons to reduce meat consumption!