I have already mentioned that you should remove yourself from junk mail mailing lists (you can do this at organizedinnovations.com/resources.html). And that you should open your mail over a shredder and garbage can.
But here is one extra step to take to reduce paper. When you receive a bill or statement in the mail, open it and remove the extra paper the company has added to the envelope. Toss it or shred it immediately so that all you have left is the bill/statement and the billing return address envelope.