Preparing for a dramatic reading is appreciably more demanding than for a straight-forward Reading of the Word in worship. It is more like a scripted play than a monologue. Both a solid familiarity with the text and a sense for communicating its meaning are required. With the dramatic reading, each reader must work their timing and rhythm with the other readers.
Ideally, the purpose of rehearsal is to get the readers to the point where they are comfortable and confident with the material. This will vary with the experience of the individuals involved.
Each reader should become acquainted with the text before the first rehearsal. This involves 1] going through the text to understand its meaning, and 2] considering the ways in which that meaning can best be communicated.
Rehearsal is the time to bring this work together and shape it into a cohesive whole. Effective presentation of the dramatic reading depends mostly on establishing the rhythm and pacing among the readers.