Gather experience... Look at what you should not look at. A feeling of anxiety is the sure and certain evidence that you should do this.
When you do 'Before Sunset,' you know while it's a limited audience, there was a very small group of people that love 'Before Sunrise.' You feel a certain pressure to make sure that you uphold a level of quality that has been a bar. You set a bar and you have to at least match it.
Acted drama requires surrender of one's self, sympathetic absorption in the play as it develops.