Imagination is the fountainhead of any creative process. Only when a team of people including poets, writers, directors, actors, scene designers, and producers, put their inventive imagination to use that a movie can take shape.
Imagination is such an indispensable tool in the hands of an actor that if an actor stops using it, the only option left for him would be to quit acting as a profession. You should, by all means, strive to develop your imagination. Different people have different types of imagination. Some people are blessed with a kind of imagination that always works for them, whether they are awake or asleep. Some have an imagination that immediately spurs to action when desired. As an actor, if you lack imagination, you need at least to have the knack to develop it else, you are doomed to fail.
When you observe the nature of gifted people, it would disclose to you a way to control the emotion needed in a part. When you choose to access the power of imagination, it helps you realize exactly which emotion would help you portray the character you are playing. Then, you will need to stimulate your creative fantasy so that it stirs up your emotion or affective memory. Creative fantasy helps you go beyond the reach of consciousness, and access the elements of emotions you may have experienced in the past. You can then re-group the emotions to correspond to the images that creative fantasy brings to your mind. Therefore, creative fantasy is a fundamental and a necessary gift for an actor.
Imagination can really work wonders. It opens up to a world of sights, sounds, and feelings at any given moment. Our inner eye can help us see, or rather imagine, a variety of visual images, living creatures, human faces, landscapes, objects, settings and so forth. Our inner ear can help us hear all sorts of melodies, voices, intonations, and so forth. We can feel things in imagination whenever our sensation and emotion memory prompts us.
There are actors who imagine well through visuals and there are actors who imagine well through sounds. The first category of actors mentioned here is gifted with an especially fine inner vision and the second with sensitive inner hearing. Whether you imagine passively or take an active part in those dreams, it will temporarily pull you away from your reality and draw you into your own mental projection.
As an actor, when you put your imagination to use for feeling a scene, you must thoroughly work out everything that you imagine. What you imagine must be able to answer all the questions (when, where, why, how) so that you can drive your inventive faculties on to achieving a more and more definite picture of a make-believe existence.