I'm currently in rehearsals for a one-act play that is part of six that will be produced later this summer. A few days ago, we had our first rehearsal, following the initial readthrough of the script a week earlier.
Before any reading or blocking, the director sat us all down to talk through some points about the script and each of our characters. Keep in mind that this is a 15 to 20-minute play; the lead character has only about 50 lines, I have 23, and a couple of actresses have about 5 to 10 each.
The director asked each of us about our character, what that character was like, the hopes and dreams, some background, and other pointed questions. For the most part, our answers paralled those of the director, who'd had collaborative discussions with the playwright.
Later, as we walked through the blocking, the director reminded us of these attributes, in order that we could incorporate them into our roles.
This director had done his homework with the script, and the scriptwriter had done his job in that he had successfully conveyed critical information to the actors about their characters through the dialogue. The fact that we all had begun to develop our characters along his envisioned lines showed that, even with limited numbers of speeches.
It's not luck that allows actors to understand what the scriptwriter is thinking, it's clear writing. The successful writer carefully develops unique characters that leap off the pages into the performers' imaginations.
Getting this experience first-hand as an actor is a terrific lesson in how to achieve similar results with your own scripts. Plus, acting is fun!