The scenario (sogetto) is nothing but the tissue of scenes woven from a plot, containing abbreviated hints at an action, divided into acts and scenes, which have to be acted and spoken in an extemporaneous manner by the player. On the margin there are indications where each character has to enter, and a broken line indicates where the actors make their exits. At the top of each scenario is mentioned the place (e.g., Rome, Naples, Genoa, Leghorn, etc.), where the action of the play is supposed to take place. …

The manager (corago) or most experienced actor of the troupe should rehearse (concertare) the scenario before it is acted, so that the players may now the contents of the play and understand where the dialogue should end, and so that they may discover, while rehearsing, where a new bit of comic business (lazzo) could befitted in. The one who conducts the rehearsal, then, will have the task not only of reading the scenario, but of explaining the characters, their names and quality, the subject matter, the place of action, the various stage houses; he will have to plant the lazzi and all the necessary details, giving attention to those things which are needed in the play, such as letters, purses, daggers, and other properties mentioned at the end of the scenario.
For instance, he will say: "The play we are going to perform is La Trappolaria; the characters are Tartaglia, father of Fedelindo and master of Coviello; Policinella, a slave-dealer, and Turchetta, his slave; the courtesan Isabella with her servants, the parasite Pespice and Pimpinella; the Captain and his servant Pasquariello; Mme. Laura, wife of Tartaglia, who comes from abroad with a servant; a salesman…" Then he will define the stage-houses, assigning to Tartaglia the first house on the right, to Policinella the second on the left, and to Isabella the second on the right. Next he will expound the plot.

The actors must, above all, be careful not to make a mistake with regard to the country where the action is going to take place; they should realize whence they come, and for what purpose; the proper names must be kept well in mind, since it would be a grave error and unpardonable impropriety for one actor to speak of being in Rome and another in Naples; or that they character who comes from Spain should say Germany; or for the father to forget the name of his son or the lover that of his beloved…

Moreover, the actors must pay attention to the distribution of the houses, so that each player may know his own house, for it would be too ridiculous for anyone to knock at or enter into somebody else's house instead of his own: one would regard such a person as a booby or a drunkard…

Next the director explains the lazzi and plot complications, saying: "Here such a lazzo is needed, there such a metaphor, such a hyperbole, or irony." In this manner he will go through all the lazzi and witticisms, giving the actors advice as to how to overcome individual difficulties, trying to avoid, as much as possible, improprieties, though they can sometimes not be prevented. …

The characters should take care not to run into each other when they enter, which can more easily happen in improvised than in premeditated plays…though to leave the scene upstage and to enter it down-stage is an infallible rule, unless it is changed by some necessity.

Improvised comedy has this advantage over premeditated plays: one can remedy empty and silent scenes, each player being able to continue in the tenor of the preceding scene and to talk until the entrance of the next player marks the signal for the exit of the one who has been on the stage.
After they have been told what they have to do with regard to their entrances, the treatment and termination of scenes, the actors will be able to run through the scenes and among themselves to rehearse to new lazzo or new material of their own invention. It will be advisable, however, not to deviate from the plot to such an extant that they actors cannot find their way back into it. It must be avoided that the audience, due to extended and obtrusive comic business, lose the thread of the plot or have difficulty in grasping it again. …

All the players should be assembled to listen, and the attitude that they know this comedy by heart or that they have acted it on previous occasions, should be discouraged. For it might very well be that other names and places were chosen when the actors played the same plot under a different director….

After having rehearsed the scenario, the actors ought to think about bringing in something already prepared or something specially designed for the play in question…some fact, story, or thing, either applicable to this particular play or some universal thins, which they have memorized to be used in any play, such as conceits on first entrances, desperations, dialogues, reproaches, greetings, comparisons….Which night is to follow upon some scene, care must be taken to indicate this in the preceding scene by saying: "It's getting dark,"…and so also when dawn comes and morning approaches.

[trans, Salvatore J. Castiglione]