Think about what the word “revise” means: to see again.
When you write something, it’s a good idea to put it aside for awhile. Studies have shown that three days is optimal, but I realize most of us don’t have that much time. If you can put space between you and your work even for a few hours, chances are you will come back to it with new eyes. Sometimes when I have done this, my reaction has been, “I wrote this?” And I don’t mean that in a good way.
Never write in anger. Especially if you feel you have to write a critical piece, I urge you to put it away for as long as you can before sending it. Think about the person receiving it; try to anticipate the reaction. It might be a good time for some judicious editing—or deciding not to send the piece at all.