Avoid the use of Never.
Avoid the use of Always.
Refrain from saying you are wrong.
You can say your idea is mistaken.
Don't disagree with obvious truths.
Attack the idea not the person.
Use many rather than most.
Use some rather than many.
The use of often allows for exceptions.
The use of generally allows for exceptions.
Quote sources and numbers.
If it is just an opinion, admit it.
Do not present opinion as facts.
Stress the positive.
You do not need to win every battle to win the war.
Concede minor or trivial points.
Avoid bickering, quarreling, and wrangling.
Keep your perspective