Put the emphasis on the error and not the person when you are attempting to resolve a situation where someone else made a mistake.
For example, say 'The attachment didn't come through. Please try sending it again' instead of 'You didn't send the attachment.' It may not seem like a big deal, but blaming someone makes them more likely to react defensively or aggressively.
#general
In the same way, when you enter into a discussion with another person, instead of "You are wrong, you are wrong," you should say "I do not agree with this statement."
Thanks, that's really good advice. I have repeatedly noticed how the ability to properly talk to a person allows you to get the maximum benefit.