Never give an opinion 

without taking one first 

   That's a motto I'm trying to keep. And, of course, I often fail to keep it. But, perhaps if I keep trying, I will turn the corner, and keep the rule more often than not. A corollary is to always show respect for the other person's opinion. Don't just listen to it, waiting for the opening and chance to tear it apart. Instead, listen reflectively and acknowledge any good points and praise the other person for their opinion.