The 2002 General Instruction of the Roman Missal (GIRM) speaks very specifically about silence before and during the liturgy. We read: “Sacred silence also, as part of the celebration, is to be observed at the designated times. Its purpose, however, depends on the time it occurs in each part of the celebration. Thus within the Act of Penitence and again after the invitation to pray, all recollect themselves; but at the conclusion of a reading or a homily, all meditate briefly on what they have heard; then after Communion, they praise and pray to God in their hearts.”
There should also be silence before the liturgy: “Even before the celebration itself, it is commendable that silence be observed in the church, in the sacristy, in the vesting room, and in adjacent areas, so that all may dispose themselves to carry out the sacred action in a devout and fitting manner” (No. 45).
Though not mentioned in the GIRM, there is a long practice of maintaining silence within the body of the church after Mass. Some churches erupt in noise once Mass is over. This destroys the atmosphere of prayer that is conducive and appropriate to private prayer after Mass.
How does a pastor encourage an atmosphere of silence? By giving good example himself. If he is walking up and down the aisles and engaging in audible conversations, then he is giving a wrong cue to the people. Even worse is the practice of priests, deacons and ministers chatting in the sanctuary area before Mass.
Some carefully worded admonitions during the announcements period toward the end of Mass would go a long way toward encouraging the correct atmosphere regarding silence. In my experience, people are often unaware of the distracting nature of their chatting, and they are open to correction.
One of the devices I myself use is always to respond in a whisper when people come to talk to me in the church before Mass. Mostly, they take the hint (that they should be speaking quietly) and are not offended.