I am not an actor. Studying how actors prepare their craft, I am left with a question regarding character development. As a writer, I have concrete ideas as to any given characters background/bio, what motivates them, their fears, wants, desires, etc. I also have very concrete ideas as to why the character is even in the story to begin with. Talk about the juxtaposition between how the writer envisioned his character, and how an actor or director can change that and the impact it has on story.
Actors usually start with the script, looking for clues on the characters in the writing. A writer’s vision of the story, along with the characters, usually transpires in the story, and a good actor will get a lot of it from just working on the script and rehearsing. That being said, both plays and screenplays are collaborative arts, and the director, as well as the actors, will also bring their own vision to your words. I believe it’s a good thing, as long as you’re working with people whose work you trust and respect.
Besides the script, actors use other means to explore character, including working from the outside in (maybe with a prop or costume mentioned in the script), writing bios, or doing their own research on the subject matter, time period, social background, etc. Directors also have their own interpretation. Their choice of set and staging for plays, or camera angles, lighting and editing for movies, can make a huge difference in how the story is delivered. Some things are out of the writer’s hands of course. You may not have a say on the director or the actors, or you may have a chance to give your input every step of the way. It’s the same for film actors, though. Unless they are a recognizable name actor who has a say in the final edit of the film, their vision of a character can be transformed in the editing room.
If you have talented people working on your script, though, you’ll be surprised at all the depth and nuance they find in your words. Actually, many screenwriters used actors to workshop their scripts.