"Performance is like a sailboat," explains Ethan Hawke. Don't over plan your performance. Let it happen. Get caught in the moment. And when you give yourself the freedom the experiment and explore your character then some happy accidents can happen in your performance.
"Tap into your character's obsessions," suggests Matthew McConaughey. Understand your character's motivations and connect to their emotions. You want to bring their soul to life and treat them like they are a real person. Ask yourself how this character exist outside the script? What would this character be like if they were someone you know and lived in your world?
More help for actors at the links below:
Free Online Acting School