How can I make my performance more naturalistic?

A vital aspect of a naturalistic performance is the idea of motivation. You have to remember that in a naturalistic performance, you are trying to present your character as a real person, with real desires and real emotions, speaking the lines for the first time, no matter how many times you may have spoken them. You should ask yourself questions like these:"Why is my character in this room at this particular time, talking to this particular person?""What does my character want from this interaction?""What does my character need from this interaction?"
There should be a clear motivation behind every movement you make and every word you say on stage. A really helpful way to explore answers to such questions is to use a rehearsal technique called 'hot seating'. Place yourself on stage with your classmates as an audience. Assume the role and persona of your character, while your classmates ask you questions about your life, backstory, childhood, aspirations, etc.. Respond to these questions as your character. Try to be accurate with regards to any information from the text but don't worry if you feel like you don't know the exact answer to a question. Just try to respond in the way you think your character would. You should hopefully start to understand the mindset and psyche of your character more and this will make your performance feel more 'real' and appear more naturalistic.