I notice that a lot of my coworkers print emails for recordkeeping purposes. While that activity does use excess paper and toner, hurting the environment in a way I can't force them to change, I can do my part to help. I use the lightweight "Century Gothic" typeface in a size no larger than 10 pts. Any extra information in my emails (signatures, confidentiality clauses, etc.) are printed in an even smaller grey font because it takes less toner to produce and a small font uses less paper for long print jobs. That's my "one thing" at work.