Talk low, talk slow, and don't say too much.
— John Wayne

First learn the meaning of what you say, and then speak.
Epictetus oratory quote

He who knows little knows enough if he knows how to hold is tongue.
— Italian Proverbs

The trouble with me is that I like to talk too much.
— William Howard Taft

People who know little are usually great talkers, while men who know much say little.
— oratory quotation by Jean-Jacques Rousseau