In Ben Franklin's autobiography (on gutenberg.org, I think), he points out how he learned to get along better by prefacing things with "I think..." or "It seems like..." etc. That and observing one's own blunders and learning from them :) can help -- I mean, recognizing that none of us knows everything, we are limited and can be wrong. Listening, realizing that others have perspectives and experiences that we don't always have, and their input can increase our overall understanding.

I've also found it very helpful to practice phrasing things as questions instead of strong statements -- keeps less egg on my face, in times when I just didn't know all the facts. I.e., instead of "that is a bad idea", say maybe "wouldn't that lead to problems [, like maybe x, y or maybe z?". Then people can reply to the question instead of feeling attacked and attacking back.