Where the homily is concerned, there is a lot to say. First, a definition:
24. Through the course of the liturgical year the homily sets forth the mysteries of faith and the standards of the Christian life on the basis of the sacred text. Beginning with the Constitution on the Liturgy, the homily as part of the liturgy of the word has been repeatedly and strongly recommended and in some cases it is obligatory. As a rule it is to be given by the one presiding.  The purpose of the homily at Mass is that the spoken word of God and the liturgy of the Eucharist may together become “a proclamation of God’s wonderful works in the history of salvation, the mystery of Christ.”  Through the readings and homily Christ’s paschal mystery is proclaimed; through the sacrifice of the Mass it becomes present.  Moreover Christ himself is always present and active in the preaching of his Church. 
While the readings are the usual foundation for the homily, other texts of the Liturgy are a possible source, too:
Whether the homily explains the text of the Sacred Scriptures proclaimed in the readings or some other text of the Liturgy,  it must always lead the community of the faithful to celebrate the Eucharist actively, “so that they may hold fast in their lives to what they have grasped by faith.”  From this living explanation, the word of God proclaimed in the readings and the Church’s celebration of the day’s Liturgy will have greater impact. But this demands that the homily be truly the fruit of meditation, carefully prepared, neither too long nor too short, and suited to all those present, even children and the uneducated. 
The homily must always lead to the faithful’s active celebration of the Eucharist. That’s a surprising place for participation to show up, but there you have it. Note also the great demands placed on the homiletic preacher, especially that these words and this message be the fruit of a spiritual life.
One might ask, “What about moral sermons?” Clearly these are not homilies, by definition. And when a homily is required, it probably can’t be replaced by a sermon.
At a concelebration, the celebrant or one of the concelebrants as a rule gives the homily. 
25. On the prescribed days, that is, Sundays and holydays of obligation, there must be a homily in all Masses celebrated with a congregation, even Masses on the preceding evening; the homily may not be omitted without a serious reason.  There is also to be a homily in Masses with children and with special groups. 
A homily is strongly recommended on the weekdays of Advent, Lent, and the Easter season for the sake of the faithful who regularly take part in the celebration of Mass; also on other feasts and occasions when a large congregation is present. 
I cannot recall a parish that didn’t have homilies at daily Mass even in ordinary time. Is this your experience?
The priest may preach from the chair, but not sitting down:
26. The priest celebrant gives the homily, standing either at the chair or at the ambo. 
No announcements at homily time, this seems crystal clear:
27. Any necessary announcements are to be kept completely separate from the homily; they must take place following the prayer after Communion. 
We covered a lot of particulars in the series on Fulfilled in Your Hearing (see sidebar). For more discussion on homilies, I refer interested readers there. Otherwise, any questions on the universal Church’s expectations for the homily? See any problems?