My first acting experience was in first grade at the one-room schoolhouse I attended in South Jersey through third grade. I was a sailor in a chorus line singing "Anchors Aweigh." The other half-dozen or so kids had blue navy uniforms; all that was left for me was a white uniform that helped inaugurate my lifelong tradition of not fitting in....
My first "serious" role was as a senior in high school, playing the reporter in The Man Who Came to Dinner. I am sure that I auditioned for this only because I was trying to emulate (and probably please) my father, who had been playing leads in a variety of community theater (then called "Little Theater") productions around South Jersey. (He writes about the origin of his love for theater in his memoirs) I had little idea of what an actor needs to do, but I gained at least one attitude from watching my father's performances: to attempt to be as natural as possible. Over the years, I learned a lot about what that actually meant (for instance, it's more about being "real" than "natural") and how to achieve it.
Different actors can be effective with different techniques, but I think the following is a fair summary of what all good acting (other than shtick, which has its place) demands:*
The core of acting is reacting—listening, engaging with what fellow actors say and do, and, within the context of your character, responding from honest places in yourself that connect with what is happening on stage. Ideally, a play should be fresh each performance—an ensemble experience in which no role is completely fixed but in wc each performance shifts a bit because there are slightly different energies, each player is reacting in the moment, and actors keep making new discoveries within the overall arcs of their characters and the play as rehearsed. A scene or beat hinges on an intention that raises the stakes for one's character, and there is no single legitimate line reading.
I don't pretend all actors, successful or not, subscribe to every detail of this summary, but I do think that only the unusual actor, probably born with uncommon intuitive powers that work on stage, will be effective without them. They seem to me embedded in all acting schools that gained currency in the 20th century--Stanislavsky, Michael Chekhov, Meisner, the Actor's Studio, and so on, and I have been able successfully to coach inexperienced actors in such a spirit. What happens, alas, with most aspiring actors who have little training (and often little confidence) is that they resort during early rehearsals and line study at home to trying to find the "right" line reading for all their lines and to perform their roles in exactly the same way every time. (Certainly this is how I started out, and it probably wasn't til my thirties that I began to learn better.) Aside from the fact that there is no single "correct" line reading (delivery will vary according to intention, unique performance vibes, and maybe whether the actor has an upset stomach), and aside from whatever artificial energy an actor reproduces every performance, this approach produces bland performances that lack energy. Especially in amateur performances, an audience may still enjoy such ritualized behavior, but whether they know it or not, they would enjoy the same play more with freshness each performance.
In all productions in which I've been involved, some of the actors have had little or no training, and this can create major problems in developing a convincing performance with an ensemble tone. The key to success or failure here, it seems to me, is the attitude and ability of the director. I still struggle with constructively managing this problem when I work with a director who does not embrace the principles I describe above. On the other hand, when working with a director who does understand (and support) them, the rehearsal and performance processes can be exhilarating.
My best experience was in 2004 as Willy Loman in Death of a Salesman at the Ivoryton Playhouse in Connecticut. Most of the cast was skilled and committed to making the play work, and our director, Dave Conoway, despite little experience as a director, understood and supported the kind of acting approach I cite here while having the skills to manage me and the rest of the cast when theoretical, temperamental or interpretive problems arose.
*I suspect the same principles apply to musicals, but I have been in only a couple, many years ago, and I am not clear how much the rehearsal process might differ.