Using Eric Morris' the being state, the trick is to blur the line between self and character such that you are "being" the character. Meisner recommends feeling what your character feels, it's a very there technique. I have turned down theatrical roles because I was not interested in being in the headspace of the character.

one of the seminal works of "method acting" (which is one school of acting - in a nutshell, it holds that an actor can most effectively portray emotion by actually entering (to a certain degree) the desired emotional state. there's more to it than that.) is Konstantin Stanislavski's An Actor Prepares. it's quite readable, go get it. :)