Background & History
The letters, songs and music were written on separate bits of paper, partly so the actor would be spared having to learn them, and this may explain why some of them are missing from the First Folio, as the different bits of paper might have gone astray. The same might well apply to the Prologues and Epilogues, some of which may only have been read at the first performance of a play.
From Henslowe's Diary we learn that when the theatres were open the company performing at the Rose Theatre (near the Globe) would present a different play every day, six days a week. A play would be repeated for as long as it was popular; after that it would drop out of the repertoire. Most plays were performed about twelve times over a two year period before they became obsolete, and they introduced a new play into the repertoire at an average of one every two weeks.
With this hectic schedule, there would be little time for 'rehearsals' in the modern sense of the word, and no time for an elongated preparation period. Since there was a different play put on every day, it would not be practical to 'rehearse' a play in advance of its day of performance, when a large portion of the morning would be taken up with memorising (or re-memorising) the play to be performed that afternoon. Because an actor would not know which plays were to be performed in an upcoming week; how often they would be performed, or if there was only going to be one performance, there was not the modern actor's need to keep the whole repertoire in his head at all times.
When the King's Men (the company of which Shakespeare was a member) went to Hampton Court to entertain King James at Christmas, they put on 18 different plays in 22 days, so preparations would have been practical, not philosophical.
Acting from a Cue Script
The actors were not given a complete copy of the play that was to be performed, but they worked from Parts (a Cue Script being a section of a complete part). They were written out (some believe by the actors themselves) on sheets of paper, and each complete speech was prefaced by a few words as a "Cue" or "Q" (both are mentioned in the First Folio). How to make up a Role in the original way is included with each purchase of a Part or Beginnings.
Like the television actors today who work on daily "soaps", there was little time for rehearsal, for any moment not taken up with actually acting would be spent memorising. Preparation would mostly be private, with the actor bringing to the performance decisions based on the words they had to say, not on an understanding of what was going on. This suggests that all the clues necessary for performing the part would need to be in the actor's own lines, for there was little time for debate and discussion discussion - it is all in the text, not the context.
It is fascinating to see the information that the original actor would have seen, and it concentrates the mind as to what may or may not be important, when preparing or studying a part. All the OSC productions and workshops used such Parts and Cue Scripts.
Clues to Acting from the Folio