Most beginning actors find that one of the most difficult problems is that of staying in character when other actors are speaking.
The way to stay in character, whether the actor is speaking lines or waiting for his next cue is to listen.

TO LISTEN IN CHARACTER IS ONE OF THE MOST IMPORTANT SECRETS TO SUCCESSFUL ACTING.

This means that the actor must learn to concentrate on what the other actors are saying, with the same attention , as though he was hearing the lines for the first time.

The importance of thinking lines is so that they will appear spontaneous. This same thinking and concentration must be used by the actor on the lines he hears from other actors.
He must also learn the cue lines (the last three (3) or four (4) words of the actor's speech which preceeds his own lines.

Another important technigue to learn is how to LISTEN and RESPOND.
The concentration that is required for an actor to silently think the lines and react is vital to his training as a convincing and consistent actor.
When an actor is able to make his whole body respond emotionally, he is giving total response. This requires a high degree of tension and energy.

In learning to make the total body respond, sometimes it is helpful for the actor to do a toning exercise just to give the muscles the practice of tensing.
This is done by first clenching the fists as tightly as possible, then releasing them.
Next, tense the arms, then relax.
Then tense the toes, feet, and legs by driving the heels into the floor and locking the knees tightly, then relax.
Last, tense the entire body from head to toe, then relax.

The artist is the one who reacts to whatever he encounters, deeply and powerfully.
This is the imaginative energy of learning - to feel as the characters must in the drama of life created in a play.

The actor must build to the emotional climax with unrestrained feeling.
If the intensity of feeling is honest and powerful, THE AUDIENCE WILL BE MOVED TO BELIEVE.