CHAPTER ONE of the Screenwriting Essentials online tutorial & workbook discuss STORY CONCEPT and idea.
From the very first IMAGE you see on the screen you are telling your audience what to expect in this visual journey they are about to embark upon. I always say that writing is about choices and your choices for telling your movie start with that very first image.
Every artist faces this decision making process, whether it's an oil painter, a photographer or YOU, the screenwriter. Visually speaking, you compose each scene - you choose the location (what does IT say to your viewer). You choose the apparel (to some extent) of your characters - ie are they goth, business, glam or a slouch? You choose ALL the words they speak. What is going on beneath the words they actually say? Are they saying "I love you" while they batter each other with trash from a garbage can?
Now that doesn't mean that you become a 'control freak' as a writer. You leave many, many choice to the director and the actors and the set designer and the locations manager. BUT, when it's IMPORTANT to our understanding of the story or the emotional landscape of the heroine/hero you put the DETAILS in your script. You CHOOSE the words that make it clear.
There is a power and a responsibility in every story choice you make as a writer. With proper planning - you can learn to revel in the choosing - not be frozen in place - unable to act or stymied with indecision.
I hope this helps. And I do wish you luck with your new screenplay. Let me know when you've completed your script. I'd love to read your work!