The best images are mirrors in which we see ourselves.
I want something more to my life:
I'm afraid for a loved one:
I have to let someone go, even though it's ripping me to pieces:
The best actors wear the same expressions on their faces as we do while we watch them. The writer's job is to make the reader wear the same expression as he/she reads. To elicit emotion from a black and white page is no easy task, but that's what makes writing so difficult - and so important.
As your reader likely won't have access to actors to perform the script live in front of them, you must rely on dialogue and action to make your point. This means keeping your reader on his/her toes and making your characters pop from page one.
Once you've crafted your character and the situation in which they find themselves, what's your poster image? What's a defining snapshot (literally - imagine a photo) that tells us as much as possible about who your character is and what they're up against? What makes them iconic?
How is your beginning the promise of your end? How will you bookend your story? In what way has your protagonist changed?
Of course, it's not enough to think of defining images for your work at large. Can you think of a defining image in each individual sequence? Or scene?
Many actors use a device known as sense memory which reminds them of similar circumstances to those in your script. If you have a scene in which they have to commit an illegal act, they might place themselves back to when they were 17 and sneaked into a neighbor's yard to steal a lawn gnome.
Bottom line, actors become characters through accurately evoking emotion. You become a writer the same way. So when you write a scene and you're not sure how to make a character react, base your conflict on what you've seen in real life, not other films. You relate to it. Your actors will relate to it.
Most importantly, your audience will relate to it, and they'll be back for more from you.