By Constantin Stanislavsky:

"Love the art in yourself and not yourself in the art."
"Create your own method. Don't depend slavishly on mine. Make up something that will work for you! But keep breaking traditions, I beg you."
"Remember: there are no small parts, only small actors."
"The person you are is a thousand times more interesting than the actor you could ever hope to be."
"Remember this practical piece of advice: Never come into the theatre with mud on your feet.  Leave your dust and dirt outside.  Check your little worries, squabbles, petty difficulties with your outside clothing - all the things that ruin your life and draw attention away from your art - at the door."

By Sanford Meisner:

"Pick up the impulse - not the cue."
"Play.  PLAY.  It's a play."
"Acting is the ability to live truthfully under the given imaginary circumstances."
"Acting is behavior."

By Uta Hagen:

"Theoretically, the actor must be more sound in mind and body than other people, since he/she learns to understand the psychological problems of human beings when putting his/her own passions, his/her loves, his/her fears, and rages to work in the service of the characters he/she plays.  He/she will learn to face himself/herself - to hide nothing from himself/herself - and to do so takes an INSATIABLE CURIOSITY ABOUT THE HUMAN CONDITION."

"The Feeling of Reality - Performance and Authenticity" by Pulitzer-prize winning playwright, Ayad Akhtar

"The Importance of Daydreaming" by Kristin Linklater, creator of the Linklater Voice Technique