One of the things I emphasize to my screenwriting students is that once you determine the basic building blocks of your story:
Character / Action / Goal / Adversary
that is, if you have a MOTIVATED Character STRUGGLING to do an Action in order to achieve a LIFE or DEATH Goal opposed by a WORTHY Adversary, you have the minimum requirements for a story.
However, the trick is to make sure that your Character's Action is a. a verb and b. applies to the ENTIRE story. Also, your character's Goal must be a noun and also apply to the ENTIRE story.
This is harder than it appears. Often I find students' attempts at this story template results in a confusion between goal and action. For example, not being rigorous about the grammar, as pedantic as it might appear, can get you into trouble. Deciding that a character's goal is "to succeed" rather than "success" can confuse you when you try and determine what he's going to do to succeed. Because the goal "to succeed" is a verb, rather than a noun. Being rigorous about the grammar forces you to ensure you actually have actions and goals in place.
The other difficulty is making sure that the actions and goals chosen actually apply to the entire story. Often instead of a dramatic action that applies to the entire story, student writers often pick what I call activities that the character may do during the course of the plot. But they haven't distilled all the different activities into a fundamental dramatic action.
Why is that important and in the writer's interest? Because by distilling the various ideas for activities into a fundamental dramatic action, the writer now has a guidepost by which he or she can determine the validity of any other idea they might have as they write the script. Can they draw a line from the idea they have for a cool scene back to the fundamental action and therefore the story's underlying template? (Which my students now just call CAGA.) If so, then the idea might work. If not, then either the idea has to be discarded or at least altered OR the underlying story template must be in order to accommodate it.
By being rigorous about your character's underlying action and goal in particular, you give yourself a better chance of writing a story that remains dramatically consistent. Lack of consistency with the underlying template of your story runs it off the rails.