I have had a lot of questions lately about how to stay in character or how to keep from forgetting my lines. These topics are closely related as they are caused by the same thing: a lapse in concentration by the actor.
I find that the biggest cause of breaks in concentration is self-awareness (being self-conscious). When the actor switches from being the character (concentrating on the stimuli of the scene and reacting moment by moment--what the famous acting teachers Meisner and Adler called "staying in the moment") to thinking about what he or she looks like and/or is doing, the actor has lost it; and it is visible to all observing him-- just as though the character is a pasted-on image that has been ripped off of the actor. Thus our challenge as actors is to forget ourselves for in doing so we are then open to be the character.
Playing the moment means that the actor does not think about what has already happened in his or her performance. Nor does he or she thing about what is to come later in the play. It means that the actor is fully concentrating on the moment of the scene that is present. Without the concentration to do that, the actor cannot respond successfully and will give a poor performance.
The actors concentration begins with the actor being fully confident of having the lines learned perfectly.
Then the actor focuses his or her eyes on the other actors. Watch Marlon Brando, James Dean, Paul Newman, Clint Eastwood, John Wayne or other famous actors. Watch how they focus on the other actors. Their eyes steady and burning into their scene partners demonstrates stong concentration and leads to effecive performances.
Being self-conscious is always detrimental to the actor. It is essential to having good emotional responses to the stimuli in the scene that the actor is free from inhibitions that cause him or her to be worried about what people will think about what they are doing in their performance. Such an impediment to acting effectively must be avoided. And it will be avoided by those actors who work to rid themselves of being self-conscious. Being in many plays and studying in the proper acting classes will bring the actor a sense of security and effectiveness in their acting.