Shut up is still considered by most people as an expression of rudeness, but hey, however, used in everyday conversation and tone in spoken indicating the severity or indifference. Therefore, a screaming child until his parents closed, we imagine, be admonished, but in adult conversation the following observation: "Oh, come on, shut up I'm trying to be serious!" would be harmless in the request for cooperation. More formally, "Shut up" and "Shut up," as the orders call for greater respect.
And "Quiet!" gravity has a dramatic and almost all medieval on your account. Less impressive is "Pay attention now, please!" and "I can have your attention please?" On a more easy when you want peace of mind that can only say: "Do you mind?" or "set time" and for a humorous effect using "OK, let's have some silence." Two terms used in special circumstances "Order, order," he said in a debating chamber and "Silence in court!" used in a court of law.
Of course, silence can also mean, as we keep to yourself or revealing secrets or personal feelings. We are silent when mom or protect private information. When others tell us that an important part of the news they do not want publicity surrounding them we advise: "Keep it under your hat, did not spread at all, do not tell anyone" or just "keep it to yourself."