The Introduction to the Lectionary of the Mass
The present Order of Readings for Mass, then, is an arrangement of biblical readings that provides the faithful with a knowledge of the whole of God’s word, in a pattern suited to the purpose. Throughout the liturgical year, but above all during the seasons of Easter, Lent, and Advent, the choice and sequence of readings are aimed at giving the faithful an ever-deepening perception of the faith they profess and of the history of salvation.98
Accordingly, the Order of Readings corresponds to the requirements and interests of the Christian people."
From The Introduction to the Lectionary of the Mass. This is a resource found on the Archdiocesan website and outlines the importance of the Lectionary and readings for the Church's Liturgical year. Though a 44 page pdf file, still useful for readers of the word.
The link is here
Below is the Otari Parish Readers manual used in conjunction with training which is provided by the Readers group for new readers.