One of the things I've observed in my career as a writer of plays and screenplays and as a producer of new scripts is the critical importance of that very first test of new material with other artist/collaborators. In other words, there's a lot at stake when your new script is being given voice for the first time. This phase in the life of a new screenplay or play is--for you, the writer--often a make or break moment.
When I founded the Playwrights Theatre of New Jersey many years ago, my primary motivation was to help writers with this delicate first "release" of their new script to the wider world. I knew that the actors assembled to give the work its first read had to be carefully chosen for each role and had to be very good at bringing words on the page to life with little or no rehearsal. I knew that to do otherwise would risk the writer concluding that they'd lost their hearing, as playwright Wendy Wasserstein told me when she described her response to a first reading of a new play of hers. Some of the actors were simply not right for the roles and she had trouble recognizing the play she'd just finished writing.
Or as playwright and Academy Award-winning screenwriter John Patrick Shanley told me when he first released his wonderful play Danny and the Deep Blue Sea: "I thought [it] was a dead loss on the basis of a reading. I heard the reading and I said, 'Well, I guess I was wrong. I thought it was good.' Then I did another reading and I thought, 'Well, it's better.' And then I got some good people and I thought, 'All right, now we're talking!' So you have to be very careful not to write off a [script] on the basis of a bad reading."
Just realize that your initial launch with new material--allowing other artists to connect with it for the first time--is more significant than you may at first realize. As eager as you may be to hear your script come to life for the first time, be careful to gather actors that are talented, are a good match for the character they're reading, and know what their character's function is in the play or screenplay.