An actor has a wide range of tools to charm an audience, throw together ideas, and develop situations and characters for the stage. One of the main things that i believe an actor uses is narration. Narration is a technique whereby one or more performers speak directly to the audience to tell a story, give information or comment on the action of the scene or the motivations of characters. Characters may narrate, or a performer who is not involved in the action can carry out the role of 'narrator'. This is a great technique as it keeps the audience informed in were the act is moving and also involved in the act.
Method acting is another greatly used technique. Method acting is a technique were the actor analyse the motivations and emotions of the character they are playing in order to personify him or her with psychological realism and emotional authenticity. Using the Method, an actor recalls emotions or reactions from his or her own life and uses them to identify with the character being portrayed. This in itself helps the audience fall into the realm of the act.
Another major technique that is used by actors is presentational acting. Presentational acting refers to a relationship between actor and audience, whether by direct address or indirectly by specific use of language, looks, gestures or other signs indicating that the character or actor is aware of the audience's presence. (Shakespeare's use of punning and wordplay, for example, often has this function of indirect contact.)
In representational acting, "actors want to make us "believe" they are the character; they pretend." The illusion of the fourth wall with the audience as voyeurs is striven for.
Improvisation is a difficult technique. It is both a good and bad technique to engage an audience as there is no need to remember lines so the actor never drops out of character to think about lines keeping the audience totally interested but then again it could go bad as the actor could not work...