I've joked to my colleagues that someday I'm going to write a book about acting, called "Suck Less, Act Better."
I made a few notes on my theory of acting while sitting in the Burger King at Rosslyn a few months ago. The following is a condensation of these notes:
When it comes to finding an objective, consider the relationship between your character and the others. It's all a question of who's got the power. It may be within a household (family dynamics, husband & wife, parent & child, etc) or a kingdom, or what have you. It all boils down to power dynamics and control.
A character is either in control or being controlled.
The person in control wants at the very least to maintain control, or has to decide whether or not to risk expanding their control at the potential cost of losing control.
The person being controlled wants at the very least to survive under the conditions dictated by the controller, or has to decide whether or not to risk usurping control from the controller at the potential cost of worsening their condition.
Or, as a variation, the person is somewhere in the middle, controlled by some, in control of others, and slides up or down the spectrum.
Consider the plays of Pinter, Mamet, Shepard, etc. and the life-or-death power dynamics that govern the plots. Preferably over a chocolate shake.