If you have a gift with words, learn to keep your mouth shut; when you speak, punctuate with pause; and when you have nothing to say, say nothing.
Spiced with silence your words taste deep and sound strong. Without it they are mere gurgle.
More than this, meaningful silence can, by itself, echo louder than voice. It can, if you know what you do, shout that which you do not say. Remember Franz Kafka: “Now the Sirens have a still more fatal weapon than their song, namely their silence. And though admittedly such a thing has never happened, still it is conceivable that someone might possibly have escaped from their singing; but from their silence certainly never.” 
Many years ago, when I used to be young, busy and concerned not to lose face, I discovered by error the amazing force of keeping silent for a moment. At that time, the evenings, after many hours of television work, instead of going home to rest, I gave public conferences on various subjects at an open university. I used to speak with ease, on my feet, which compensated the very light preparation of the subjects. It had to happen though; that evening, I rushed to the University, up to my rostrum... and realised, in front of some three hundred people that I did not even remember the title of the conference.
Believe me, this was horror! Paralysed, I kept however looking round and round, with a brave face and a sunken heart, in the mad hope that I will remember. I did not.
After some fifty seconds, maybe one interminable minute I did not find better than to ask the public with a full voice:
“So, anyone knows what our subject is today?”
The void was such that a couple of people volunteered the precious information. I sucked it in and continued cautiously, thoughtfully:
“What could I tell you about this vast subject?”...
I went on developing my line of thinking in loud voice, sketched a plan, started elaborating the points, warmed up and spoke for an hour and a half. In the end I still felt tense, but I was saved, the ordeal passed.
Something happened then that shocked me though. A number of people came from the audience to congratulate me and to tell me what a charming, talented speaker I was, what a great orator I will be. I thought they were delirious or mocking me. But they seemed sincerely impressed by something. What was that? Certainly not my bad preparation. I had to think.
In time I understood: it was the weight of silence.
At times you need to establish your credibility, your authority to be listened to, with an audience which does not know you. Nobody introduced you to help. All you have is you, as you appear and do here and now: Hic Rhodus, hic saltus!
For such occasions learn to use a spell of silence: look firmly, with intelligence into all the eyes, smile if adequate, let the tension of emptiness grow for some 40 seconds (that is very long in a large crowded audience) and then speak calmly.
Your silence passes many messages; one is that you are somebody, not nobody, a person able to face a crowd and to wait. This is an almost biological power of the big secure animal looking at harmless ones. People understand or better said they feel. After this, you have a better chance to be listened to. But you will want to follow your speech punctuating your words with silence:
to leave time to understand,
time for news to sink in,
time to let other people give some sign of response or to intervene.
Time also to listen to what other people say.
This is a strong, dangerous tool, for the skilled to use and not for the feint of heart. Without exercise and judgement it can blow in your face.
 The Silence of the Sirens,. In Franz Kafka: The Complete Stories, Glatzer Ed., New York: Schocken, 1979, p. 431.
 Hic Rhodus, hic saltus’ (Rhodes is here, jump here!) a saying translated from Aesop’s fable about a braggart who kept explaining how high he used to jump in far-away Rhodes until someone invited him to show what he can here and now.