Ideas are fun to play with and they are the basis for mapping out your story. There are many different schools of thought related to mapping out a story but ultimately you just need to pick one and stick to it, even if that process is no process. If you are one of those that don’t believe in the three act structure or in a “cookie cutter” format then more power to you, go do your thing. However if you choose the path of writing your script based on one of the many formatting processes such as Joseph Campbell’s The Hero’s Journey then just make sure you know the concept inside and out. The more you study it and the more familiar you get with the story beats the easier it will be for you to fill those beats in. It takes time, but this is time you must afford yourself in the process of making a film.
There is a reason these formulas work and even when most films feel fresh and new, most likely you can break it down into one of the many formulaic story building processes. Hollywood has adapted a process because the box office speaks volumes. Most movie goers don’t understand how or why a film is good or bad other than on superficial terms but the studio system has made a business of know why and most of the time they get it right if you consider the box office numbers. You could say it’s just as much equal marketing as it is formula but if you strip away either or then a pattern still emerges. In short just as the studios need equal part marketing and structure, a writer needs structure and talent. Structure you can learn but to creatively think of ideas that will be interesting to a mass audience either takes luck or talent. Ideas might be a dime a dozen but good ideas are far and few between.